Multiple independent trials

Questions involving repeated independent trials with the same probability structure, calculating probabilities of specific sequences or patterns.

8 questions · Moderate -0.5

2.03a Mutually exclusive and independent events
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CAIE S1 Specimen Q7
11 marks Standard +0.3
7 The faces of a biased die are numbered \(1,2,3,4,5\) and 6 . The probabilities of throwing odd numbers are all the same. The probabilities of throwing even numbers are all the same. The probability of throwing an odd number is twice the probability of throwing an even number.
  1. Find the probability of throwing a 3 . \includegraphics[max width=\textwidth, alt={}, center]{34ae4f06-d485-4138-82d8-902b70f08995-10_51_1563_495_331}
  2. The die is thrown three times. Find the probability of throwing two 5 s and one 4 .
  3. The die is thrown 100 times. Use an approximation to find the probability that an even number is thrown at most 37 times.
OCR MEI S1 Q2
6 marks Standard +0.8
2 Each packet of Cruncho cereal contains one free fridge magnet. There are five different types of fridge magnet to collect. They are distributed, with equal probability, randomly and independently in the packets. Keith is about to start collecting these fridge magnets.
  1. Find the probability that the first 2 packets that Keith buys contain the same type of fridge magnet.
  2. Find the probability that Keith collects all five types of fridge magnet by buying just 5 packets.
  3. Hence find the probability that Keith has to buy more than 5 packets to acquire a complete set.
OCR MEI S1 2016 June Q2
7 marks Moderate -0.8
2 In a hockey league, each team plays every other team 3 times. The probabilities that Team A wins, draws and loses to Team B are given below.
  • \(\mathrm { P } (\) Wins \() = 0.5\)
  • \(\mathrm { P } (\) Draws \() = 0.3\)
  • \(\mathrm { P } (\) Loses \() = 0.2\)
The outcomes of the 3 matches are independent.
  1. Find the probability that Team A does not lose in any of the 3 matches.
  2. Find the probability that Team A either wins all 3 matches or draws all 3 matches or loses all 3 matches.
  3. Find the probability that, in the 3 matches, exactly two of the outcomes, 'Wins', 'Draws' and 'Loses' occur for Team A.
OCR MEI D1 2016 June Q1
8 marks Moderate -0.8
1 Pierre knows that, if he gambles, he will lose money in the long run. Nicolas tries to convince him that this is not the case. Pierre stakes a sum of money in a casino game. If he wins then he gets back his stake plus the same amount again. If he loses then he loses his stake. Nicolas says that Pierre can guarantee to win by repeatedly playing the game, even though the probability of winning an individual game is less than 0.5 . His idea is that Pierre should bet in the first game with a stake of \(\pounds 100\). If he wins then he stops, as he will have won \(\pounds 100\). If he loses then he plays again with a stake of \(\pounds 200\). If he wins then he has lost \(\pounds 100\) and won \(\pounds 200\). This gives a total gain of \(\pounds 100\), and he stops. If he loses then he plays again with a stake of \(\pounds 400\). If he wins this time he has lost \(\pounds 100\) and \(\pounds 200\) and won \(\pounds 400\). This gives a total gain of \(\pounds 100\), and he stops. Nicolas's advice is that Pierre simply has to continue in this way, doubling his stake every time that he loses, until he eventually wins. Nicolas says that this guarantees that Pierre will win \(\pounds 100\). You are to simulate what might happen if Pierre tries this strategy in a casino game in which the probability of him winning an individual game is 0.4 , and in which he has \(\pounds 1000\) available.
  1. Give an efficient rule for using 1-digit random numbers to simulate the outcomes of individual games, given that the probability of Pierre winning an individual game is 0.4 .
  2. Explain why at most three random digits are needed for one simulation of Nicolas's strategy, given that Pierre is starting with \(\pounds 1000\).
  3. Simulate five applications of Nicolas's strategy, using the five sets of three 1-digit random numbers in your answer book.
  4. Summarise the results of your simulations, giving your mean result.
AQA S1 2007 January Q5
10 marks Moderate -0.8
5 Dafydd, Eli and Fabio are members of an amateur cycling club that holds a time trial each Sunday during the summer. The independent probabilities that Dafydd, Eli and Fabio take part in any one of these trials are \(0.6,0.7\) and 0.8 respectively. Find the probability that, on a particular Sunday during the summer:
  1. none of the three cyclists takes part;
  2. Fabio is the only one of the three cyclists to take part;
  3. exactly one of the three cyclists takes part;
  4. either one or two of the three cyclists take part.
AQA S1 2010 January Q4
12 marks Moderate -0.8
4 Each school-day morning, three students, Rita, Said and Ting, travel independently from their homes to the same school by one of three methods: walk, cycle or bus. The table shows the probabilities of their independent daily choices.
\cline { 2 - 4 } \multicolumn{1}{c|}{}WalkCycleBus
Rita0.650.100.25
Said0.400.450.15
Ting0.250.550.20
  1. Calculate the probability that, on any given school-day morning:
    1. all 3 students walk to school;
    2. only Rita travels by bus to school;
    3. at least 2 of the 3 students cycle to school.
  2. Ursula, a friend of Rita, never travels to school by bus. The probability that: Ursula walks to school when Rita walks to school is 0.9 ; Ursula cycles to school when Rita cycles to school is 0.7 . Calculate the probability that, on any given school-day morning, Rita and Ursula travel to school by:
    1. the same method;
    2. different methods.
AQA AS Paper 2 2022 June Q14
7 marks Moderate -0.8
14 Yingtai visits her local gym regularly. After each visit she chooses one item to eat from the gym's cafe.
This could be an apple, a banana or a piece of cake.
She chooses the item independently each time.
The probability that Yingtai chooses each of these items on any visit is given by: $$\begin{aligned} \mathrm { P } ( \text { Apple } ) & = 0.2 \\ \mathrm { P } ( \text { Banana } ) & = 0.35 \\ \mathrm { P } ( \text { Cake } ) & = 0.45 \end{aligned}$$ For any four randomly selected visits to the gym, find the probability that Yingtai chose: 14
  1. at least one banana.
    [0pt] [2 marks]
    14
  2. the same item each time.
    14
  3. apple twice and cake twice
Edexcel S1 Q5
13 marks Moderate -0.8
The students in a large Sixth Form can choose to do exactly one of Community Service, Games or Private Study on Wednesday afternoons. The probabilities that a randomly chosen student does Games and Private Study are \(\frac{3}{8}\) and \(\frac{1}{5}\) respectively. It may be assumed that the number of students is large enough for these probabilities to be treated as constant.
  1. Find the probability that a randomly chosen student does Community Service. [2 marks]
  2. If two students are chosen at random, find the probability that they both do the same activity. [3 marks]
  3. If three students are chosen at random, find the probability that exactly one of them does Games. [3 marks]
Two-fifths of the students are girls, and a quarter of these girls do Private Study.
  1. Find the probability that a randomly chosen student who does Private Study is a boy. [5 marks]