OCR MEI Further Statistics A AS 2018 June — Question 2

Exam BoardOCR MEI
ModuleFurther Statistics A AS (Further Statistics A AS)
Year2018
SessionJune
TopicDiscrete Probability Distributions
TypeCalculate E(X) from given distribution

2 In a quiz, competitors have to match 5 landmarks to the 5 British counties which the landmarks are in. The random variable \(X\) represents the number of correct matches that a competitor gets, assuming that the competitor guesses randomly. The probability distribution of \(X\) is given in the following table.
\(r\)012345
\(\mathrm { P } ( X = r )\)\(\frac { 11 } { 30 }\)\(\frac { 3 } { 8 }\)\(\frac { 1 } { 6 }\)\(\frac { 1 } { 12 }\)0\(\frac { 1 } { 120 }\)
  1. Explain why \(\mathrm { P } ( X = 4 )\) must be 0 .
  2. Explain how the value \(\frac { 1 } { 120 }\) for \(\mathrm { P } ( X = 5 )\) is calculated.
  3. Draw a graph to illustrate the distribution.
  4. Find each of the following.
    • \(\mathrm { E } ( X )\)
    • \(\operatorname { Var } ( X )\)
    • Find \(\mathrm { P } ( X > \mathrm { E } ( X ) )\).
    • There are 12 competitors in the quiz. Assuming that they all guess randomly, find the probability that at least one of them gets all five matches correct.