Questions — Edexcel S2 (562 questions)

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Edexcel S2 Q1
5 marks Easy -2.0
A large dental practice wishes to investigate the level of satisfaction of its patients.
  1. Suggest a suitable sampling frame for the investigation. [1]
  2. Identify the sampling units. [1]
  3. State one advantage and one disadvantage of using a sample survey rather than a census. [2]
  4. Suggest a problem that might arise with the sampling frame when selecting patients. [1]
Edexcel S2 Q2
7 marks Moderate -0.8
The random variable R has the binomial distribution B(12, 0.35).
  1. Find P(R ≥ 4). [2]
The random variable S has the Poisson distribution with mean 2.71.
  1. Find P(S ≤ 1). [3]
The random variable T has the normal distribution N(2.5, 5²).
  1. Find P(T ≤ 18). [2]
Edexcel S2 2004 January Q1
5 marks Easy -1.8
A large dental practice wishes to investigate the level of satisfaction of its patients.
  1. Suggest a suitable sampling frame for the investigation. [1]
  2. Identify the sampling units. [1]
  3. State one advantage and one disadvantage of using a sample survey rather than a census. [2]
  4. Suggest a problem that might arise with the sampling frame when selecting patients. [1]
Edexcel S2 2004 January Q2
7 marks Easy -1.3
The random variable \(R\) has the binomial distribution B(12, 0.35).
  1. Find P(\(R \geq 4\)). [2]
The random variable \(S\) has the Poisson distribution with mean 2.71.
  1. Find P(\(S \leq 1\)). [3]
The random variable \(T\) has the normal distribution N(25, \(5^2\)).
  1. Find P(\(T \leq 18\)). [2]
Edexcel S2 2004 January Q3
9 marks Moderate -0.3
The discrete random variable \(X\) is distributed B(\(n\), \(p\)).
  1. Write down the value of \(p\) that will give the most accurate estimate when approximating the binomial distribution by a normal distribution. [1]
  2. Give a reason to support your value. [1]
  3. Given that \(n = 200\) and \(p = 0.48\), find P(\(90 \leq X < 105\)). [7]
Edexcel S2 2004 January Q4
10 marks Moderate -0.8
  1. Write down two conditions needed to be able to approximate the binomial distribution by the Poisson distribution. [2]
A researcher has suggested that 1 in 150 people is likely to catch a particular virus. Assuming that a person catching the virus is independent of any other person catching it,
  1. find the probability that in a random sample of 12 people, exactly 2 of them catch the virus. [4]
  2. Estimate the probability that in a random sample of 1200 people fewer than 7 catch the virus. [4]
Edexcel S2 2004 January Q5
13 marks Moderate -0.3
Vehicles pass a particular point on a road at a rate of 51 vehicles per hour.
  1. Give two reasons to support the use of the Poisson distribution as a suitable model for the number of vehicles passing this point. [2]
Find the probability that in any randomly selected 10 minute interval
  1. exactly 6 cars pass this point, [3]
  2. at least 9 cars pass this point. [2]
After the introduction of a roundabout some distance away from this point it is suggested that the number of vehicles passing it has decreased. During a randomly selected 10 minute interval 4 vehicles pass the point.
  1. Test, at the 5\% level of significance, whether or not there is evidence to support the suggestion that the number of vehicles has decreased. State your hypotheses clearly. [6]
Edexcel S2 2004 January Q6
13 marks Standard +0.3
From past records a manufacturer of ceramic plant pots knows that 20\% of them will have defects. To monitor the production process, a random sample of 25 pots is checked each day and the number of pots with defects is recorded.
  1. Find the critical regions for a two-tailed test of the hypothesis that the probability that a plant pot has defects is 0.20. The probability of rejection in either tail should be as close as possible to 2.5\%. [5]
  2. Write down the significance level of the above test. [1]
A garden centre sells these plant pots at a rate of 10 per week. In an attempt to increase sales, the price was reduced over a six-week period. During this period a total of 74 pots was sold.
  1. Using a 5\% level of significance, test whether or not there is evidence that the rate of sales per week has increased during this six-week period. [7]
Edexcel S2 2004 January Q7
18 marks Moderate -0.3
The continuous random variable \(X\) has probability density function $$\text{f}(x) = \begin{cases} kx(5 - x), & 0 \leq x \leq 4, \\ 0, & \text{otherwise,} \end{cases}$$ where \(k\) is a constant.
  1. Show that \(k = \frac{3}{56}\). [3]
  2. Find the cumulative distribution function F(\(x\)) for all values of \(x\). [4]
  3. Evaluate E(\(X\)). [3]
  4. Find the modal value of \(X\). [3]
  5. Verify that the median value of \(X\) lies between 2.3 and 2.5. [3]
  6. Comment on the skewness of \(X\). Justify your answer. [2]
Edexcel S2 2009 January Q1
11 marks Standard +0.3
A botanist is studying the distribution of daisies in a field. The field is divided into a number of equal sized squares. The mean number of daisies per square is assumed to be 3. The daisies are distributed randomly throughout the field. Find the probability that, in a randomly chosen square there will be
  1. more than 2 daisies, [3]
  2. either 5 or 6 daisies. [2]
The botanist decides to count the number of daisies, \(x\), in each of 80 randomly selected squares within the field. The results are summarised below $$\sum x = 295 \quad \sum x^2 = 1386$$
  1. Calculate the mean and the variance of the number of daisies per square for the 80 squares. Give your answers to 2 decimal places. [3]
  2. Explain how the answers from part (c) support the choice of a Poisson distribution as a model. [1]
  3. Using your mean from part (c), estimate the probability that exactly 4 daisies will be found in a randomly selected square. [2]
Edexcel S2 2009 January Q2
9 marks Easy -1.2
The continuous random variable \(X\) is uniformly distributed over the interval \([-2, 7]\).
  1. Write down fully the probability density function f(x) of \(X\). [2]
  2. Sketch the probability density function f(x) of \(X\). [2]
Find
  1. E(\(X^2\)), [3]
  2. P(\(-0.2 < X < 0.6\)). [2]
Edexcel S2 2009 January Q3
7 marks Moderate -0.3
A single observation \(x\) is to be taken from a Binomial distribution B(20, \(p\)). This observation is used to test \(H_0 : p = 0.3\) against \(H_1 : p \neq 0.3\)
  1. Using a 5\% level of significance, find the critical region for this test. The probability of rejecting either tail should be as close as possible to 2.5\%. [3]
  2. State the actual significance level of this test. [2]
The actual value of \(x\) obtained is 3.
  1. State a conclusion that can be drawn based on this value giving a reason for your answer. [2]
Edexcel S2 2009 January Q4
12 marks Moderate -0.8
The length of a telephone call made to a company is denoted by the continuous random variable \(T\). It is modelled by the probability density function $$\text{f}(t) = \begin{cases} kt & 0 \leqslant t \leqslant 10 \\ 0 & \text{otherwise} \end{cases}$$
  1. Show that the value of \(k\) is \(\frac{1}{50}\). [3]
  2. Find P(\(T > 6\)). [2]
  3. Calculate an exact value for E(\(T\)) and for Var(\(T\)). [5]
  4. Write down the mode of the distribution of \(T\). [1]
It is suggested that the probability density function, f(\(t\)), is not a good model for \(T\).
  1. Sketch the graph of a more suitable probability density function for \(T\). [1]
Edexcel S2 2009 January Q5
9 marks Moderate -0.3
A factory produces components of which 1\% are defective. The components are packed in boxes of 10. A box is selected at random.
  1. Find the probability that the box contains exactly one defective component. [2]
  2. Find the probability that there are at least 2 defective components in the box. [3]
  3. Using a suitable approximation, find the probability that a batch of 250 components contains between 1 and 4 (inclusive) defective components. [4]
Edexcel S2 2009 January Q6
14 marks Standard +0.3
A web server is visited on weekdays, at a rate of 7 visits per minute. In a random one minute on a Saturday the web server is visited 10 times.
    1. Test, at the 10\% level of significance, whether or not there is evidence that the rate of visits is greater on a Saturday than on weekdays. State your hypotheses clearly.
    2. State the minimum number of visits required to obtain a significant result.
    [7]
  1. State an assumption that has been made about the visits to the server. [1]
In a random two minute period on a Saturday the web server is visited 20 times.
  1. Using a suitable approximation, test at the 10\% level of significance, whether or not the rate of visits is greater on a Saturday. [6]
Edexcel S2 2009 January Q7
13 marks Standard +0.3
A random variable \(X\) has probability density function given by $$\text{f}(x) = \begin{cases} -\frac{2}{9}x + \frac{8}{9} & 1 \leqslant x \leqslant 4 \\ 0 & \text{otherwise} \end{cases}$$
  1. Show that the cumulative distribution function F(x) can be written in the form \(ax^2 + bx + c\), for \(1 \leqslant x \leqslant 4\) where \(a\), \(b\) and \(c\) are constants. [3]
  2. Define fully the cumulative distribution function F(x). [2]
  3. Show that the upper quartile of \(X\) is 2.5 and find the lower quartile. [6]
Given that the median of \(X\) is 1.88
  1. describe the skewness of the distribution. Give a reason for your answer. [2]
Edexcel S2 2011 January Q1
10 marks Moderate -0.3
A disease occurs in 3\% of a population.
  1. State any assumptions that are required to model the number of people with the disease in a random sample of size \(n\) as a binomial distribution. [2]
  2. Using this model, find the probability of exactly 2 people having the disease in a random sample of 10 people. [3]
  3. Find the mean and variance of the number of people with the disease in a random sample of 100 people. [2]
A doctor tests a random sample of 100 patients for the disease. He decides to offer all patients a vaccination to protect them from the disease if more than 5 of the sample have the disease.
  1. Using a suitable approximation, find the probability that the doctor will offer all patients a vaccination. [3]
Edexcel S2 2011 January Q2
6 marks Moderate -0.5
A student takes a multiple choice test. The test is made up of 10 questions each with 5 possible answers. The student gets 4 questions correct. Her teacher claims she was guessing the answers. Using a one tailed test, at the 5\% level of significance, test whether or not there is evidence to reject the teacher's claim. State your hypotheses clearly. [6]
Edexcel S2 2011 January Q3
11 marks Moderate -0.3
The continuous random variable \(X\) is uniformly distributed over the interval \([-1,3]\). Find
  1. E(\(X\)) [1]
  2. Var(\(X\)) [2]
  3. E(\(X^2\)) [2]
  4. P(\(X < 1.4\)) [1]
A total of 40 observations of \(X\) are made.
  1. Find the probability that at least 10 of these observations are negative. [5]
Edexcel S2 2011 January Q4
6 marks Standard +0.3
Richard regularly travels to work on a ferry. Over a long period of time, Richard has found that the ferry is late on average 2 times every week. The company buys a new ferry to improve the service. In the 4-week period after the new ferry is launched, Richard finds the ferry is late 3 times and claims the service has improved. Assuming that the number of times the ferry is late has a Poisson distribution, test Richard's claim at the 5\% level of significance. State your hypotheses clearly. [6]
Edexcel S2 2011 January Q5
13 marks Moderate -0.3
A continuous random variable \(X\) has the probability density function f(\(x\)) shown in Figure 1. \includegraphics{figure_1} Figure 1
  1. Show that f(\(x\)) = \(4 - 8x\) for \(0 \leqslant x \leqslant 0.5\) and specify f(\(x\)) for all real values of \(x\). [4]
  2. Find the cumulative distribution function F(\(x\)). [4]
  3. Find the median of \(X\). [3]
  4. Write down the mode of \(X\). [1]
  5. State, with a reason, the skewness of \(X\). [1]
Edexcel S2 2011 January Q6
16 marks Standard +0.3
Cars arrive at a motorway toll booth at an average rate of 150 per hour.
  1. Suggest a suitable distribution to model the number of cars arriving at the toll booth, \(X\), per minute. [2]
  2. State clearly any assumptions you have made by suggesting this model. [2]
Using your model,
  1. find the probability that in any given minute
    1. no cars arrive,
    2. more than 3 cars arrive.
    [3]
  2. In any given 4 minute period, find \(m\) such that P(\(X > m\)) = 0.0487 [3]
  3. Using a suitable approximation find the probability that fewer than 15 cars arrive in any given 10 minute period. [6]
Edexcel S2 2011 January Q7
13 marks Standard +0.3
The queuing time in minutes, \(X\), of a customer at a post office is modelled by the probability density function $$\text{f}(x) = \begin{cases} kx(81 - x^2) & 0 \leqslant x \leqslant 9 \\ 0 & \text{otherwise} \end{cases}$$
  1. Show that \(k = \frac{4}{6561}\). [3]
Using integration, find
  1. the mean queuing time of a customer, [4]
  2. the probability that a customer will queue for more than 5 minutes. [3]
Three independent customers shop at the post office.
  1. Find the probability that at least 2 of the customers queue for more than 5 minutes. [3]
Edexcel S2 2002 June Q2
5 marks Easy -1.2
A random sample \(X_1, X_2, \ldots, X_n\) is taken from a finite population. A statistic \(Y\) is based on this sample.
  1. Explain what you understand by the statistic \(Y\). [2]
  2. Give an example of a statistic. [1]
  3. Explain what you understand by the sampling distribution of \(Y\). [2]
Edexcel S2 2002 June Q3
9 marks Moderate -0.3
The continuous random variable \(R\) is uniformly distributed on the interval \(\alpha \leq R \leq \beta\). Given that \(\mathrm{E}(R) = 3\) and \(\mathrm{Var}(R) = \frac{25}{3}\), find
  1. the value of \(\alpha\) and the value of \(\beta\), [7]
  2. \(\mathrm{P}(R < 6.6)\). [2]