Edexcel S2 2009 January — Question 1

Exam BoardEdexcel
ModuleS2 (Statistics 2)
Year2009
SessionJanuary
TopicPoisson Distribution
TypeGoodness-of-fit test for Poisson

  1. 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,
  2. either 5 or 6 daisies. 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 $$\sum x = 295 \quad \sum x ^ { 2 } = 1386$$
  3. Calculate the mean and the variance of the number of daisies per square for the 80 squares. Give your answers to 2 decimal places.
  4. Explain how the answers from part (c) support the choice of a Poisson distribution as a model.
  5. Using your mean from part (c), estimate the probability that exactly 4 daisies will be found in a randomly selected square.