CAIE S1 2011 June — Question 2

Exam BoardCAIE
ModuleS1 (Statistics 1)
Year2011
SessionJune
TopicConditional Probability
TypeStandard Bayes with discrete events

2 When Ted is looking for his pen, the probability that it is in his pencil case is 0.7 . If his pen is in his pencil case he always finds it. If his pen is somewhere else, the probability that he finds it is 0.2 . Given that Ted finds his pen when he is looking for it, find the probability that it was in his pencil case.