Critical Path Analysis

1 A major project has been divided into a number of tasks, as shown in the table. The minimum time required to complete each task is also shown. \section*{Answer space for question 1}

1 hour 15 minutes \section*{} Additional Materials:
Answer Booklet/Paper
Graph Paper
List of Formulae (MF9) \section*{READ THESE INSTRUCTIONS FIRST} If you have been given an Answer Booklet, follow the instructions on the front cover of the Booklet.
Write your Centre number, candidate number and name on all the work you hand in.
Write in dark blue or black pen.
You may use a soft pencil for any diagrams or graphs.
Do not use staples, paper clips, highlighters, glue or correction fluid.
Answer all the questions.
Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place in the case of angles in degrees, unless a different level of accuracy is specified in the question.
Where a numerical value for the acceleration due to gravity is needed, use \(10 \mathrm {~m} \mathrm {~s} ^ { - 2 }\).
The use of an electronic calculator is expected, where appropriate.
You are reminded of the need for clear presentation in your answers.
At the end of the examination, fasten all your work securely together.
[0pt] The number of marks is given in brackets [ ] at the end of each question or part question.
The total number of marks for this paper is 50.
Questions carrying smaller numbers of marks are printed earlier in the paper, and questions carrying larger numbers of marks later in the paper.

4. \begin{figure}[h] \end{figure} Direct roads between six cities, A, B, C, D, E and F, are represented in Figure 3. The weight on each arc is the time, in minutes, required to travel along the corresponding road. Floyd's algorithm is to be used to find the complete network of shortest times between the six cities.
An initial route matrix is given in the answer book.

1. Set up the initial time matrix.
2. Perform the first iteration of Floyd's algorithm. You should show the time and route matrices after this iteration. The final time matrix after completion of Floyd's algorithm is shown below.

   \cline { 2 - 7 } \multicolumn{1}{c|}{}	A	B	C	D	E	F
   A	-	57	95	147	63	220
   B	57	-	72	204	120	197
   C	95	72	-	242	158	125
   D	147	204	242	-	84	275
   E	63	120	158	84	-	191
   F	220	197	125	275	191	-

   A route is needed that minimises the total time taken to traverse each road at least once.
   The route must start at B and finish at E .
3. Use an appropriate algorithm to find the roads that will need to be traversed twice. You should make your method and working clear.
4. Write down the length of the route.

1 The table shows the activities involved in a project, their durations and their precedences.

1. Draw an activity on arc network for these activities.
2. Mark on your diagram the early time and the late time for each event. Give the critical activities.

1 The table shows the activities involved in a project, their durations and their precedences.

1. Draw an activity on arc network for these activities.
2. Mark on your diagram the early time and the late time for each event. Give the critical activities.

6 Tariq wants to advertise his gardening services. The activities involved, their durations (in hours) and immediate predecessors are listed in the table.

1. Draw an activity network, using activity on arc, to represent the project.
2. Carry out a forward pass and a backward pass through the activity network, showing the early event time and the late event time at each vertex of your network. State the minimum project completion time and list the critical activities. Tariq does not have time to complete all the activities on his own, so he gets some help from his friend Sally.
   Sally can help Tariq with any of the activities apart from \(C , H\) and \(J\). If Tariq and Sally share an activity, the time it takes is reduced by 1 hour. Sally can also do any of \(F , G\) and \(I\) on her own.
3. Describe how Tariq and Sally should share the work so that activity \(D\) can start 5 hours after the start of the project.
4. Show that, if Sally does as much of the work as she can, she will be busy for 18 hours. In this case, for how many hours will Tariq be busy?
5. Explain why, if Sally is busy for 18 hours, she will not be able to finish until more than 18 hours from the start. How soon after the start can Sally finish when she is busy for 18 hours?
6. Describe how Tariq and Sally can complete the project together in 18 hours or less.

\includegraphics{figure_7} A project is modelled by the activity network shown in Figure 7. The activities are represented by the arcs. The number in brackets on each arc gives the time, in days, to complete the activity. Each activity requires one worker. The project is to be completed in the shortest possible time.

1. Complete Diagram 2 in the answer book to show the early and late event times. [4]
2. State the critical activities. [1]
3. On Grid 1 in the answer book, draw a cascade (Gantt) chart for this project. [4]
4. Use your cascade chart to determine a lower bound for the number of workers needed. You must justify your answer. [2]

(Total 11 marks) TOTAL FOR PAPER: 75 MARKS END

3. \begin{figure}[h] \end{figure} A project is modelled by the activity network shown in Figure 2. The activities are represented by the arcs. The number in brackets on each arc gives the time, in days, to complete the corresponding activity. Each activity requires one worker. The project is to be completed in the shortest possible time.

1. Complete Diagram 1 in the answer book to show the early event times and the late event times.
2. State the critical activities.
3. Draw a cascade (Gantt) chart for this project on Grid 1 in the answer book.
4. Use your cascade chart to determine the minimum number of workers needed to complete the project in the shortest possible time. You must make specific reference to time and activities. (You do not need to provide a schedule of the activities.)

6 Joan and Keith have to clear and tidy their garden. The table shows the jobs that have to be completed, their durations and their precedences.

1. Draw an activity on arc network for these activities.
2. Mark on your diagram the early time and the late time for each event. Give the minimum completion time and the critical activities.
3. Each job is to be done by one person only. Joan and Keith are equally able to do all jobs. Draw a cascade chart indicating how to organise the jobs so that Joan and Keith can complete the project in the least time. Give that least time and explain why the minimum project completion time is shorter.

5. (a) Draw the activity network described in this precedence table, using activity on arc and exactly two dummies.
(4) (b) Explain why each of the two dummies is necessary.
(3)

7. \begin{figure}[h] \end{figure} Figure 7 is the activity network relating to a building project. The activities are represented by the arcs. The number in brackets on each arc gives the time to complete the activity. Each activity requires one worker. The project must be completed in the shortest possible time.

1. Explain the reason for the dotted line from event 4 to event 6 as shown in Figure 7.
   (2)
2. Complete Diagram 1 in the answer book to show the early event times and the late event times.
3. State the critical activities.
4. Calculate the total float for activity G. You must make the numbers you use in your calculation clear.
5. Draw a Gantt chart for this project on the grid provided in the answer book.
6. State the activities that must be happening at time 5.5
7. Use your Gantt chart to determine the minimum number of workers needed to complete the project in the minimum time. You must justify your answer.

6. \begin{figure}[h] \end{figure} A project is modelled by the activity network shown in Figure 4. The activities are represented by the arcs. The number in brackets on each arc gives the time required, in hours, to complete the activity. The numbers in circles are the event numbers. Each activity requires one worker.

1. Explain the significance of the dummy activity
   1. from event 5 to event 6
   2. from event 7 to event 9
2. Complete Diagram 1 in the answer book to show the early event times and the late event times.
3. State the minimum project completion time.
4. Calculate a lower bound for the minimum number of workers required to complete the project in the minimum time. You must show your working.
5. On Grid 1 in your answer book, draw a cascade (Gantt) chart for this project.
6. On Grid 2 in your answer book, construct a scheduling diagram to show that this project can be completed with three workers in just one more hour than the minimum project completion time.
   (3)

4. \begin{figure}[h] \end{figure} A project is modelled by the activity network shown in Figure 5. The activities are represented by the arcs. The number in brackets on each arc gives the time, in hours, to complete the activity. Some of the early and late times for each event are shown.

1. Calculate the missing early and late times and hence complete Diagram 1 in your answer book.
2. Calculate the total float on activities D, G and I. You must make your calculations clear.
3. List the critical activities. Each activity requires one worker.
4. Calculate a lower bound for the number of workers needed to complete the project in the minimum time.
   (2)

\includegraphics{figure_5} The network in Figure 5 shows the activities that need to be undertaken to complete a project. Each activity is represented by an arc. The number in brackets is the duration of the activity in days. The early and late event times are to be shown at each vertex and some have been completed for you.

1. Calculate the missing early and late times and hence complete Diagram 2 in your answer book. [3]
2. List the two critical paths for this network. [2]
3. Explain what is meant by a critical path. [2]

The sum of all the activity times is 110 days and each activity requires just one worker. The project must be completed in the minimum time.

1. Calculate a lower bound for the number of workers needed to complete the project in the minimum time. You must show your working. [2]
2. List the activities that must be happening on day 20. [2]
3. Comment on your answer to part (e) with regard to the lower bound you found in part (d). [1]
4. Schedule the activities, using the minimum number of workers, so that the project is completed in 30 days. [3]

(Total 15 marks)

5. \begin{figure}[h] \end{figure} A project is modelled by the activity network shown in Figure 1. The activities are represented by the arcs. The number in brackets on each arc gives the time, in days, to complete the corresponding activity. Each activity requires exactly one worker. The project is to be completed in the shortest possible time.

1. Complete Diagram 1 in the answer book to show the early event times and the late event times.
2. Calculate a lower bound for the number of workers needed to complete the project in the minimum time. You must show your working.
3. Schedule the activities on Grid 1 in the answer book using the minimum number of workers so that the project is completed in the minimum time. Additional resources become available, which can shorten the duration of one of activities D, G or P by one day.
4. Determine which of these three activities should be shortened to allow the project to be completed in the minimum time. You must give reasons for your answer.

A company undertakes a project which consists of 12 activities, \(A\), \(B\), \(C\), \(\ldots\), \(L\) Each activity requires one worker. The resource histogram below shows the duration of each activity. Each activity begins at its earliest start time. The path \(ADGJL\) is critical. \includegraphics{figure_1} The company only has two workers available to work on the project. Which of the following could be a correctly levelled histogram? Tick \((\checkmark)\) one box. [1 mark] \includegraphics{figure_2} \includegraphics{figure_3} \includegraphics{figure_4} \includegraphics{figure_5}

4 Table 4.1 shows some of the activities involved in preparing for a meeting. \begin{table}[h] \end{table}

1. Draw an activity-on-arc network to represent the precedences.
2. Find the early event time and the late event time for each vertex of your network, and list the critical activities.
3. Assuming that each activity requires one person and that each activity starts at its earliest start time, draw a resource histogram.
4. In fact although activity A has duration 1 hour, it actually involves only 0.5 hours work, since 0.5 hours involves waiting for replies. Given this information, and the fact that there is only one person available to do the work, what is the shortest time needed to prepare for the meeting? Fig. 4.2 shows an activity network for the tasks which have to be completed after the meeting. \begin{figure}[h]
   \includegraphics[alt={},max width=\textwidth]{c429bfed-9241-409a-9cd5-9553bf16c9df-5_533_844_1688_294} \captionsetup{labelformat=empty} \caption{Fig. 4.2}
   \end{figure} P: Clean room
   Q: Prepare draft minutes
   R: Allocate action tasks
   S: Circulate draft minutes
   T: Approve task allocations
   U: Obtain budgets for tasks
   V: Post minutes
   W: Pay refreshments bill
5. Draw a precedence table for these activities.

3 The table lists the duration (in hours), immediate predecessors and number of workers required for each activity in a project.

1. Draw an activity network, using activity on arc, to represent the project. You should make your diagram quite large so that there is room for working.
2. Carry out a forward pass and a backward pass through the activity network, showing the early and late event times clearly at the vertices of your network. State the minimum project completion time and list the critical activities.
3. Using graph paper, draw a resource histogram to show the number of workers required each hour. Each activity begins at its earliest possible start time. Once an activity has started it runs for its duration without a break. A delay from the supplier means that the start of activity \(F\) is delayed.
4. By how much could the start of activity \(F\) be delayed without affecting the minimum project completion time? Suppose that only six workers are available after the first four hours of the project.
5. Explain carefully what delay this will cause on the completion of the project. What is the maximum possible delay on the start of activity \(F\), compared with its earliest possible start time in part (iii), without affecting the new minimum project completion time? Justify your answer.

1. A project consists of three activities \(A\), \(B\) and \(C\) An activity network for the project is shown in the diagram below. \includegraphics{figure_1} Find the value of \(x\) Circle your answer. [1 mark] 5 \quad 7 \quad 8 \quad 12
2. Find the value of \(y\) Circle your answer. [1 mark] 5 \quad 7 \quad 8 \quad 15

1. A project consists of three activities \(A\), \(B\) and \(C\) An activity network for the project is shown in the diagram below. \includegraphics{figure_1} Find the value of \(x\) Circle your answer. [1 mark] 5 \quad 7 \quad 8 \quad 12
2. Find the value of \(y\) Circle your answer. [1 mark] 5 \quad 7 \quad 8 \quad 15

1 The diagram shows the activity network and the duration, in days, of each activity for a particular project. Some of the earliest start times and latest finish times are shown on the diagram. \includegraphics[max width=\textwidth, alt={}, center]{b23828c8-01ee-4b5a-b6d2-41b7e27190d6-02_830_1447_678_301}

1. Find the values of the constants \(x , y\) and \(z\).
2. Find the critical paths.
3. Find the activity with the largest float and state the value of this float.
4. The number of workers required for each activity is shown in the table.

   Activity	\(A\)	\(B\)	\(C\)	\(D\)	\(E\)	\(F\)	\(G\)	\(H\)	\(I\)	\(J\)
   Number of workers required	4	2	3	4	2	4	3	3	5	6

   Given that each activity starts as early as possible and assuming that there is no limit to the number of workers available, draw a resource histogram for the project on Figure 1 below, indicating clearly which activities are taking place at any given time.
5. It is later discovered that there are only 9 workers available at any time. Use resource levelling to find the new earliest start time for activity \(J\) so that the project can be completed with the minimum extra time. State the minimum extra time required. (d) Number of workers \begin{figure}[h]
   \captionsetup{labelformat=empty} \caption{Figure 1} \includegraphics[alt={},max width=\textwidth]{b23828c8-01ee-4b5a-b6d2-41b7e27190d6-03_803_1330_1224_468}
   \end{figure}

3 A project consists of 11 activities \(A , B , \ldots , K\) A completed activity network for the project is shown in the diagram below. \includegraphics[max width=\textwidth, alt={}, center]{ecbeedf5-148e-40ad-b8a2-a7aa3db4a115-04_972_1604_445_219} All times on the activity network are given in days.
3

1. Write down the critical path.
   [0pt] [1 mark] 3
2. Due to an issue with the supply of materials, the duration of activity \(G\) is doubled. Deduce the effect, if any, that this change will have on the earliest start time and latest finish time for each of the activities \(I , J\) and \(K\)

1 Figure 1 below shows an activity diagram for a construction project. The time needed for each activity is given in days.

1. Find the earliest start time and latest finish time for each activity and insert their values on Figure 1.
2. Find the critical paths and state the minimum time for completion of the project.
3. On Figure 2 opposite, draw a cascade diagram (Gantt chart) for the project, assuming that each activity starts as early as possible.
4. A delay in supplies means that Activity \(I\) takes 9 days instead of 2 .
   1. Determine the effect on the earliest possible starting times for activities \(K\) and \(L\).
   2. State the number of days by which the completion of the project is now delayed.
      (1 mark) \section*{Figure 1}
      1. \includegraphics[max width=\textwidth, alt={}, center]{c4dc61a7-47ee-4d5c-bf6d-30a5da2ee8dd-02_815_1337_1573_395}
      2. Critical paths are \(\_\_\_\_\) Minimum completion time is \(\_\_\_\_\) days. QUESTION PART REFERENCE
      3. \begin{figure}[h]
         \captionsetup{labelformat=empty} \caption{Figure 2} \includegraphics[alt={},max width=\textwidth]{c4dc61a7-47ee-4d5c-bf6d-30a5da2ee8dd-03_978_1207_354_461}
         \end{figure}

4 A project is represented by the activity network below. The activity durations are given in minutes. \includegraphics[max width=\textwidth, alt={}, center]{6f64abca-108c-4b81-8ccf-124dfd9cc2f6-5_447_1020_392_246}

1. Give the reason for the dummy activity from event (3) to event (4).
2. Complete a forward pass to determine the minimum project completion time.
3. By completing a backward pass, calculate the float for each activity.
4. Determine the effect on the minimum project completion time if the duration of activity A changes from 2 minutes to 3 minutes. The duration of activity C changes to \(m\) minutes, where \(m\) need not be an integer. This reduces the minimum project completion time.
5. By considering the range of possible values of \(m\), determine the minimum project completion time, in terms of \(m\) where necessary.

3. (a) Draw the activity network described in the precedence table below, using activity on arc and exactly four dummies.
(5) Given that D is a critical activity,
(b) state which other activities must also be critical.
(2)

5.

1. Draw the activity network described in the precedence table above, using activity on arc. Your activity network must contain only the minimum number of dummies. Given that all critical paths for the network include activity H ,
2. state which activities cannot be critical.
   (2)

5 The network below represents a project using activity on arc. The durations of the activities are not yet shown. \includegraphics[max width=\textwidth, alt={}, center]{490ff276-6639-40a1-bffb-dc6967f3ab21-6_597_1257_340_386}

1. If \(C\) were to turn out to be a critical activity, which two other activities would be forced to be critical?
2. Complete the table, in the Answer Book, to show the immediate predecessor(s) for each activity. In fact, \(C\) is not a critical activity. Table 1 lists the activities and their durations, in minutes. \begin{table}[h]

   Activity	\(A\)	\(B\)	\(C\)	\(D\)	\(E\)	\(F\)	\(G\)	\(H\)	\(I\)	\(J\)
   Duration	10	15	10	5	15	5	10	15	5	15

   \captionsetup{labelformat=empty} \caption{Table 1}
   \end{table}
3. Carry out a forward pass and a backward pass through the activity network, showing the early event time and late event time at each vertex of the network. State the minimum project completion time and list the critical activities. Each activity requires one person.
4. Draw a schedule to show how three people can complete the project in the minimum time, with each activity starting at its earliest possible time. Each box in the Answer Book represents 5 minutes. For each person, write the letter of the activity they are doing in each box, or leave the box blank if the person is resting for those 5 minutes.
5. Show how two people can complete the project in the minimum time. It is required to reduce the project completion time by 10 minutes. Table 2 lists those activities for which the duration could be reduced by 5 minutes, and the cost of making each reduction. \begin{table}[h]

   Activity	\(A\)	\(B\)	\(C\)	\(E\)	\(G\)	\(H\)	\(J\)
   Cost \(( \pounds )\)	200	400	100	600	100	500	500
   New duration	5	10	5	10	5	10	10

   \captionsetup{labelformat=empty} \caption{Table 2}
   \end{table}
6. Explain why the cost of saving 5 minutes by reducing activity \(A\) is more than \(\pounds 200\). Find the cheapest way to complete the project in a time that is 10 minutes less than the original minimum project completion time. State which activities are reduced and the total cost of doing this.

3 The activities involved in a project and their durations are represented in the activity network below. \includegraphics[max width=\textwidth, alt={}, center]{a7bca340-6947-42b5-bc35-e6d429d6bed7-3_494_700_306_683}

1. Carry out a forward pass and a backward pass through the network.
2. Find the float for each activity. A delay means that the duration of activity E increases to \(x\).
3. Find the values of \(x\) for which activity E is not a critical activity.

5

1. The graphs below illustrate the precedences involved in running two projects, each consisting of the same activities \(\mathrm { A } , \mathrm { B } , \mathrm { C } , \mathrm { D }\) and E . \begin{figure}[h]
   \captionsetup{labelformat=empty} \caption{Project 1} \includegraphics[alt={},max width=\textwidth]{8eba759f-38bc-4d14-ac65-9a0ee6c79741-6_280_385_429_495}
   \end{figure} \begin{figure}[h]
   \captionsetup{labelformat=empty} \caption{Project 2} \includegraphics[alt={},max width=\textwidth]{8eba759f-38bc-4d14-ac65-9a0ee6c79741-6_255_392_429_1187}
   \end{figure}
   1. For one activity the precedences in the two projects are different. State which activity and describe the difference.
   2. The table below shows the durations of the five activities.

      Activity	A	B	C	D	E
      Duration	2	1	\(x\)	3	2

      Give the total time for project 1 for all possible values of \(x\).
      Give the total time for project 2 for all possible values of \(x\).
2. The durations and precedences for the activities in a project are shown in the table.

   Activity	Duration	Immediate predecessors
   R	2	-
   S	1	-
   T	5	-
   w	3	R, S
   X	2	R, S, T
   Y	3	R
   Z	1	W, Y

   1. Draw an activity on arc network to represent this information.
   2. Find the early time and the late time for each event. Give the project duration and list the critical activities.

4 The table shows the activities involved in a project, their durations in hours and their immediate predecessors. The activities can be represented as an activity network.

1. Use standard algorithms to find the activities that form
   You must show working to demonstrate the use of the algorithms. Only one of the paths from part (a) has a practical interpretation.
2. What is the practical interpretation of the total weight of that path? The duration of activity E can be changed. No other durations change.
3. What is the smallest increase to the duration of E that will make activity E become part of a longest path through the network?

1 [Figures 1 and 2, printed on the insert, are provided for use in this question.]
The following diagram shows an activity diagram for a building project. The time needed for each activity is given in days. \includegraphics[max width=\textwidth, alt={}, center]{0c40b693-72d3-459c-bbb7-b9584a108b8e-02_698_1321_767_354}

1. Complete the precedence table for the project on Figure 1.
2. Find the earliest start times and latest finish times for each activity and insert their values on Figure 2.
3. Find the critical path and state the minimum time for completion of the project.
4. Find the activity with the greatest float time and state the value of its float time.

1 [Figures 1 and 2, printed on the insert, are provided for use in this question.]
The following diagram shows an activity diagram for a building project. The time needed for each activity is given in days. \includegraphics[max width=\textwidth, alt={}, center]{0c40b693-72d3-459c-bbb7-b9584a108b8e-02_698_1321_767_354}

1. Complete the precedence table for the project on Figure 1.
2. Find the earliest start times and latest finish times for each activity and insert their values on Figure 2.
3. Find the critical path and state the minimum time for completion of the project.
4. Find the activity with the greatest float time and state the value of its float time.

2 A project is represented by the activity network and cascade chart below. The table showing the number of workers needed for each activity is incomplete. Each activity needs at least 1 worker. \includegraphics[max width=\textwidth, alt={}, center]{7717b4ca-45ab-4111-9f59-5a3abb04b388-2_202_565_1605_201} \includegraphics[max width=\textwidth, alt={}, center]{7717b4ca-45ab-4111-9f59-5a3abb04b388-2_328_560_1548_820}

1. Complete the table in the Printed Answer Booklet to show the immediate predecessors for each activity.
2. Calculate the latest start time for each non-critical activity. The minimum number of workers needed is 5 .
3. What type of problem (existence, construction, enumeration or optimisation) is the allocation of a number of workers to the activities? There are 8 workers available who can do activities A and B .
4. 1. Find the number of ways that the workers for activity A can be chosen.
   2. When the workers have been chosen for activity A , find the total number of ways of choosing the workers for activity B for all the different possible values of x , where \(\mathrm { x } \geqslant 1\).

Kirstie has bought a house that she is planning to renovate. She has broken the project into a list of activities and constructed an activity network, using activity on arc. \includegraphics{figure_1}

1. Construct a cascade chart for the project, showing the float for each non-critical activity. [7]
2. Calculate the float for remodelling the internal layout stating how much of this is independent float and how much is interfering float. [3]

Kirstie needs to supervise the project. This means that she cannot allow more than three activities to happen on any day.

1. Describe how Kirstie should organise the activities so that the project is completed in the minimum project completion time and no more than three activities happen on any day. [3]

4 The table lists tasks which are involved in adding a back door to a garage. The table also lists the duration and immediate predecessor(s) for each task. Each task is undertaken by one person.

1. Draw an activity on arc network for these activities.
2. Mark on your diagram the early time and the late time for each event. Give the minimum completion time and the critical activities.
3. Produce a schedule to show how two people can complete the project in the minimum time. Soon after starting activity D , the marble step breaks. Getting a replacement step adds 4 hours to the duration of activity D.
4. How does this delay affect the minimum completion time, the critical activities and the minimum time needed for two people to complete the project? \section*{Question 5 begins on page 6}

2. \begin{figure}[h] \end{figure} A project is modelled by the activity network shown in Figure 2. The activities are represented by the arcs. The number in brackets on each arc gives the time, in hours, to complete the corresponding activity.

1. Complete Diagram 1 in the answer book to show the early event times and the late event times. Each activity requires one worker and the project must be completed in the shortest possible time using as few workers as possible.
2. Calculate a lower bound for the number of workers needed to complete the project in the shortest possible time. You must show your working.
3. Schedule the activities using Grid 1 in the answer book.

\includegraphics{figure_3} A project is modelled by the activity network shown in Fig 3. The activities are represented by the edges. The number in brackets on each edge gives the time, in days, taken to complete the activity.

1. Calculate the early time and the late time for each event. Write these in the boxes on the answer sheet. [4]
2. Hence determine the critical activities and the length of the critical path. [2]
3. Obtain the total float for each of the non-critical activities. [3]
4. On the first grid on the answer sheet, draw a cascade (Gantt) chart showing the information obtained in parts (b) and (c). [4]

Each activity requires one worker. Only two workers are available.

1. On the second grid on the answer sheet, draw up a schedule and find the minimum time in which the 2 workers can complete the project. [4]

1 Which of the following statements about critical path analysis is always true? Tick ( \(\checkmark\) ) one box. All activity networks have exactly one critical path. □ All critical activities have a non-zero float. □ The first activity in a critical path has an earliest start time of zero. □ A delay on a critical activity may not delay the project. □

3 Table 3 gives the durations and immediate predecessors for the five activities of a project. \begin{table}[h] \end{table}

1. Draw an activity-on-arc network to represent the precedences.
2. Find the early and late event times for the vertices of your network, and list the critical activities.
3. Give the total and independent float for each activity which is not critical.

2. Draw the activity network described in the precedence table below, using activity on arc and exactly three dummies.

6 The table shows the tasks that have to be completed in building a stadium for a sporting event, their durations and their precedences. The stadium has to be ready within two years.

1. Draw an activity on arc network for these activities.
2. Mark on your diagram the early time and the late time for each event. Give the project duration and the critical activities. In the later stages of planning the project it is discovered that task J will actually take 9 months to complete. However, other tasks can have their durations shortened by employing extra resources. The costs of "crashing" tasks (i.e. the costs of employing extra resources to complete them more quickly) are given in the table.

   Tasks which can be completed more quickly by employing extra resources	Number of months which can be saved	Cost per month of employing extra resources (£m)
   A	2	3
   D	1	1
   C	3	3
   F	2	2
   G	2	4

3. Find the cheapest way of completing the project within two years.
4. If the delay in completing task J is not discovered until it is started, how can the project be completed in time, and how much extra will it cost?