CAIE S1 2021 November — Question 6

Exam BoardCAIE
ModuleS1 (Statistics 1)
Year2021
SessionNovember
TopicDiscrete Probability Distributions
TypeTwo unknowns from sum and expectation

6 In a game, Jim throws three darts at a board. This is called a 'turn'. The centre of the board is called the bull's-eye. The random variable \(X\) is the number of darts in a turn that hit the bull's-eye. The probability distribution of \(X\) is given in the following table.
\(x\)0123
\(\mathrm { P } ( X = x )\)0.6\(p\)\(q\)0.05
It is given that \(\mathrm { E } ( X ) = 0.55\).
  1. Find the values of \(p\) and \(q\).
  2. Find \(\operatorname { Var } ( X )\).
    Jim is practising for a competition and he repeatedly throws three darts at the board.
  3. Find the probability that \(X = 1\) in at least 3 of 12 randomly chosen turns.
  4. Find the probability that Jim first succeeds in hitting the bull's-eye with all three darts on his 9th turn.