Edexcel S2 2018 October — Question 3

Exam BoardEdexcel
ModuleS2 (Statistics 2)
Year2018
SessionOctober
TopicContinuous Probability Distributions and Random Variables
TypeExplain why not valid PDF

3. The function \(\mathrm { f } ( x )\) is defined as $$f ( x ) = \begin{cases} \frac { 1 } { 9 } ( x + 5 ) ( 3 - x ) & 1 \leqslant x \leqslant 4
0 & \text { otherwise } \end{cases}$$ Albert believes that \(\mathrm { f } ( x )\) is a valid probability density function.
  1. Sketch \(\mathrm { f } ( x )\) and comment on Albert's belief. The continuous random variable \(Y\) has probability density function given by $$g ( y ) = \begin{cases} k y \left( 12 - y ^ { 2 } \right) & 1 \leqslant y \leqslant 3
    0 & \text { otherwise } \end{cases}$$ where \(k\) is a positive constant.
  2. Use calculus to find the mode of \(Y\)
  3. Use algebraic integration to find the value of \(k\)
  4. Find the median of \(Y\) giving your answer to 3 significant figures.
  5. Describe the skewness of the distribution of \(Y\) giving a reason for your answer.