CAIE FP2 2013 June — Question 10

Exam BoardCAIE
ModuleFP2 (Further Pure Mathematics 2)
Year2013
SessionJune
TopicGeometric Distribution
TypeGame theory with alternating players

10 Jill and Kate are playing a game as a practice for a penalty shoot-out. They take alternate turns at kicking a football at a goal. The probability that Jill will score a goal with any kick is \(\frac { 1 } { 3 }\), independently of previous outcomes. The probability that Kate will score a goal with any kick is \(\frac { 1 } { 4 }\), independently of previous outcomes. Jill begins the game. If Jill is the first to score, then Kate is allowed one more kick. If Kate scores with this kick, then the game is a draw, but if she does not score then Jill wins the game. If Kate is the first to score, then she wins the game, and no further kicks are taken.
  1. Show that the probability that Jill scores on her 5th kick is \(\frac { 1 } { 48 }\).
  2. Show that the probability that Kate wins the game on her \(n\)th kick is \(\frac { 1 } { 3 \times 2 ^ { n } }\).
  3. Find the probability that Jill wins the game.
  4. Find the probability that the game is a draw.