AQA S2 2013 June — Question 5

Exam BoardAQA
ModuleS2 (Statistics 2)
Year2013
SessionJune
TopicDiscrete Probability Distributions
TypeProbability distribution from formula

5 In a computer game, players try to collect five treasures. The number of treasures that Isaac collects in one play of the game is represented by the discrete random variable \(X\). The probability distribution of \(X\) is defined by $$\mathrm { P } ( X = x ) = \left\{ \begin{array} { c l } \frac { 1 } { x + 2 } & x = 1,2,3,4
k & x = 5
0 & \text { otherwise } \end{array} \right.$$
    1. Show that \(k = \frac { 1 } { 20 }\).
    2. Calculate the value of \(\mathrm { E } ( X )\).
    3. Show that \(\operatorname { Var } ( X ) = 1.5275\).
    4. Find the probability that Isaac collects more than 2 treasures.
  1. The number of points that Isaac scores for collecting treasures is \(Y\) where $$Y = 100 X - 50$$ Calculate the mean and the standard deviation of \(Y\).