CAIE S2 2011 November — Question 7

Exam BoardCAIE
ModuleS2 (Statistics 2)
Year2011
SessionNovember
TopicContinuous Probability Distributions and Random Variables
TypeSketch or interpret PDF graph

7 \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{3629cb5c-fb4c-43b1-b43f-ce321411b814-3_385_385_982_246} \captionsetup{labelformat=empty} \caption{Fig. 1}
\end{figure} \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{3629cb5c-fb4c-43b1-b43f-ce321411b814-3_385_380_982_669} \captionsetup{labelformat=empty} \caption{Fig. 2}
\end{figure} \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{3629cb5c-fb4c-43b1-b43f-ce321411b814-3_390_378_977_1087} \captionsetup{labelformat=empty} \caption{Fig. 3}
\end{figure} \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{3629cb5c-fb4c-43b1-b43f-ce321411b814-3_390_391_977_1503} \captionsetup{labelformat=empty} \caption{Fig. 4}
\end{figure} \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{3629cb5c-fb4c-43b1-b43f-ce321411b814-3_392_391_1475_370} \captionsetup{labelformat=empty} \caption{Fig. 5}
\end{figure} \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{3629cb5c-fb4c-43b1-b43f-ce321411b814-3_392_387_1475_872} \captionsetup{labelformat=empty} \caption{Fig. 6}
\end{figure} \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{3629cb5c-fb4c-43b1-b43f-ce321411b814-3_392_389_1475_1375} \captionsetup{labelformat=empty} \caption{Fig. 7}
\end{figure} Each of the random variables \(T , U , V , W , X , Y\) and \(Z\) takes values between 0 and 1 only. Their probability density functions are shown in Figs 1 to 7 respectively.
  1. (a) Which of these variables has the largest median?
    (b) Which of these variables has the largest standard deviation? Explain your answer.
  2. Use Fig. 2 to find \(\mathrm { P } ( U < 0.5 )\).
  3. The probability density function of \(X\) is given by $$f ( x ) = \begin{cases} a x ^ { n } & 0 \leqslant x \leqslant 1
    0 & \text { otherwise } \end{cases}$$ where \(a\) and \(n\) are positive constants.
    (a) Show that \(a = n + 1\).
    (b) Given that \(\mathrm { E } ( X ) = \frac { 5 } { 6 }\), find \(a\) and \(n\).