OCR S1 2009 June — Question 8

Exam BoardOCR
ModuleS1 (Statistics 1)
Year2009
SessionJune
TopicTree Diagrams
TypeMulti-stage with stopping condition

8 A game at a charity event uses a bag containing 19 white counters and 1 red counter. To play the game once a player takes counters at random from the bag, one at a time, without replacement. If the red counter is taken, the player wins a prize and the game ends. If not, the game ends when 3 white counters have been taken. Niko plays the game once.
  1. (a) Copy and complete the tree diagram showing the probabilities for Niko. \section*{First counter} \includegraphics[max width=\textwidth, alt={}, center]{c985b9cc-a202-4d5d-a6b3-591b0560f570-4_293_426_1231_532}
    (b) Find the probability that Niko will win a prize.
  2. The number of counters that Niko takes is denoted by \(X\).
    (a) Find \(\mathrm { P } ( X = 3 )\).
    (b) Find \(\mathrm { E } ( X )\).