Edexcel S2 2016 June — Question 6

Exam BoardEdexcel
ModuleS2 (Statistics 2)
Year2016
SessionJune
TopicDiscrete Random Variables
TypeSampling distribution of mean or linear combination

6. A bag contains a large number of counters with one of the numbers 4,6 or 8 written on each of them in the ratio \(5 : 3 : 2\) respectively. A random sample of 2 counters is taken from the bag.
  1. List all the possible samples of size 2 that can be taken. The random variable \(M\) represents the mean value of the 2 counters.
    Given that \(\mathrm { P } ( M = 4 ) = \frac { 1 } { 4 }\) and \(\mathrm { P } ( M = 8 ) = \frac { 1 } { 25 }\)
  2. find the sampling distribution for \(M\). A sample of \(n\) sets of 2 counters is taken. The random variable \(Y\) represents the number of these \(n\) sets that have a mean of 8
  3. Calculate the minimum value of \(n\) such that \(\mathrm { P } ( Y \geqslant 1 ) > 0.9\)