Frequency distribution and Poisson fit

Questions that provide a frequency table of observed counts and ask whether the data support a Poisson model, typically requiring calculation of sample mean and variance from the frequency distribution.

7 questions

CAIE S2 2014 June Q8
8
  1. The following tables show the probability distributions for the random variables \(V\) and \(W\).
    \(v\)- 101\(> 1\)
    \(\mathrm { P } ( V = v )\)0.3680.3680.1840.080
    \(w\)00.51\(> 1\)
    \(\mathrm { P } ( W = w )\)0.3680.3680.1840.080
    For each of the variables \(V\) and \(W\) state how you can tell from its probability distribution that it does NOT have a Poisson distribution.
  2. The random variable \(X\) has the distribution \(\operatorname { Po } ( \lambda )\). It is given that $$\mathrm { P } ( X = 0 ) = p \quad \text { and } \quad \mathrm { P } ( X = 1 ) = 2.5 p$$ where \(p\) is a constant.
    (a) Show that \(\lambda = 2.5\).
    (b) Find \(\mathrm { P } ( X \geqslant 3 )\).
  3. The random variable \(Y\) has the distribution \(\operatorname { Po } ( \mu )\), where \(\mu > 30\). Using a suitable approximating distribution, it is found that \(\mathrm { P } ( Y > 40 ) = 0.5793\) correct to 4 decimal places. Find \(\mu\).
OCR MEI S2 2011 January Q2
2 A student is investigating the numbers of sultanas in a particular brand of biscuit. The data in the table show the numbers of sultanas in a random sample of 50 of these biscuits.
Number of sultanas012345\(> 5\)
Frequency815129420
  1. Show that the sample mean is 1.84 and calculate the sample variance.
  2. Explain why these results support a suggestion that a Poisson distribution may be a suitable model for the distribution of the numbers of sultanas in this brand of biscuit. For the remainder of the question you should assume that a Poisson distribution with mean 1.84 is a suitable model for the distribution of the numbers of sultanas in these biscuits.
  3. Find the probability of
    (A) no sultanas in a biscuit,
    (B) at least two sultanas in a biscuit.
  4. Show that the probability that there are at least 10 sultanas in total in a packet containing 5 biscuits is 0.4389 .
  5. Six packets each containing 5 biscuits are selected at random. Find the probability that exactly 2 of the six packets contain at least 10 sultanas.
  6. Sixty packets each containing 5 biscuits are selected at random. Use a suitable approximating distribution to find the probability that more than half of the sixty packets contain at least 10 sultanas.
CAIE FP2 2016 November Q9
9 The number of visitors arriving at an art exhibition is recorded for each 10 -minute period of time during the ten hours that it is open on a particular day. The results are as follows.
Number of visitors in a 10 -minute period012345678\(\geqslant 9\)
Number of 10 -minute periods2212811134710
  1. Calculate the mean and variance for this sample and explain whether your answers support a suggestion that a Poisson distribution might be a suitable model for the number of visitors in a 10-minute period.
  2. Use an appropriate Poisson distribution to find the two expected frequencies missing from the following table.
    Number of visitors in
    a 10-minute period
    012345678\(\geqslant 9\)
    Expected number of
    10 -minute periods
    1.108.7911.729.386.253.571.791.28
  3. Test, at the \(10 \%\) significance level, the goodness of fit of this Poisson distribution to the data.
Edexcel S2 2024 January Q1
  1. The manager of a supermarket is investigating the number of complaints per day received from customers.
A random sample of 180 days is taken and the results are shown in the table below.
Number of complaints per day0123456\(\geqslant 7\)
Frequency122837382917190
  1. Calculate the mean and the variance of these data.
  2. Explain why the results in part (a) suggest that a Poisson distribution may be a suitable model for the number of complaints per day. The manager uses a Poisson distribution with mean 3 to model the number of complaints per day.
  3. For a randomly selected day find, using the manager's model, the probability that there are
    1. at least 3 complaints,
    2. more than 4 complaints but less than 8 complaints. A week consists of 7 consecutive days.
  4. Using the manager's model and a suitable approximation, show that the probability that there are less than 19 complaints in a randomly selected week is 0.29 to 2 decimal places.
    Show your working clearly.
    (Solutions relying on calculator technology are not acceptable.) A period of 13 weeks is selected at random.
  5. Find the probability that in this period there are exactly 5 weeks that have less than 19 complaints.
    Show your working clearly.
Edexcel S3 2009 June Q5
5. The number of goals scored by a football team is recorded for 100 games. The results are summarised in Table 1 below. \begin{table}[h]
Number of goalsFrequency
040
133
214
38
45
\captionsetup{labelformat=empty} \caption{Table 1}
\end{table}
  1. Calculate the mean number of goals scored per game. The manager claimed that the number of goals scored per match follows a Poisson distribution. He used the answer in part (a) to calculate the expected frequencies given in Table 2. \begin{table}[h]
    Number of goalsExpected Frequency
    034.994
    1\(r\)
    2\(s\)
    36.752
    \(\geqslant 4\)2.221
    \captionsetup{labelformat=empty} \caption{Table 2}
    \end{table}
  2. Find the value of \(r\) and the value of \(s\) giving your answers to 3 decimal places.
  3. Stating your hypotheses clearly, use a \(5 \%\) level of significance to test the manager's claim.
Edexcel S2 Q7
7. A student collects data on the number of bicycles passing outside his house in 5-minute intervals during one morning.
  1. Suggest, with reasons, a suitable distribution for modelling this situation. The student's data is shown in the table below.
    Number of bicycles0123456 or more
    Frequency714102120
  2. Show that the mean and variance of these data are 1.5 and 1.58 (to 3 significant figures) respectively and explain how these values support your answer to part (a). An environmental organisation declares a "car free day" encouraging the public to leave their cars at home. The student wishes to test whether or not there are more bicycles passing along his road on this day and records 16 bicycles in a half-hour period during the morning.
  3. Stating your hypotheses clearly, test at the \(5 \%\) level of significance whether or not there are more than 1.5 bicycles passing along his road per 5-minute interval that morning.
Edexcel S2 Q2
  1. Specify a suitable model for the distribution of \(X\).
  2. Find the mean and the standard deviation of \(X\). \item A secretarial agency carefully assesses the work of a new recruit, with the following results after 150 pages: \end{enumerate}
    No of errors0123456
    No of pages163841291772
  3. Find the mean and variance of the number of errors per page.
  4. Explain how these results support the idea that the number of errors per page follows a Poisson distribution.
  5. After two weeks at the agency, the secretary types a fresh piece of work, six pages long, which is found to contain 15 errors.
    The director suspects that the secretary was trying especially hard during the early period and that she is now less conscientious. Using a Poisson distribution with the mean found in part (a), test this hypothesis at the \(5 \%\) significance level.