OCR MEI S1 2011 January — Question 5

Exam BoardOCR MEI
ModuleS1 (Statistics 1)
Year2011
SessionJanuary
TopicTree Diagrams
TypeCalculate end-outcome probability

5 Andy can walk to work, travel by bike or travel by bus. The tree diagram shows the probabilities of any day being dry or wet and the corresponding probabilities for each of Andy's methods of travel.
\includegraphics[max width=\textwidth, alt={}, center]{7df6dcad-790d-4d0e-b1a5-3371103997d9-3_732_1141_792_500} A day is selected at random. Find the probability that
  1. the weather is wet and Andy travels by bus,
  2. Andy walks or travels by bike,
  3. the weather is dry given that Andy walks or travels by bike.