CAIE S2 2024 November — Question 6

Exam BoardCAIE
ModuleS2 (Statistics 2)
Year2024
SessionNovember
TopicContinuous Probability Distributions and Random Variables
TypeFind parameter from expectation

6 The time, \(X\) hours, taken by a large number of people to complete a challenge is modelled by the probability density function given by $$f ( x ) = \left\{ \begin{array} { c l } \frac { 1 } { x ^ { 2 } } & a \leqslant x \leqslant b
0 & \text { otherwise } \end{array} \right.$$ where \(a\) and \(b\) are constants.
  1. State what the constants \(a\) and \(b\) represent in this context.
  2. Show that \(a = \frac { b } { b + 1 }\).
    It is given that \(\mathrm { E } ( X ) = \ln 3\).
  3. Show that \(b = 2\) and find the value of \(a\).
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  4. Find the median of \(X\).