CAIE S1 2020 November — Question 4

Exam BoardCAIE
ModuleS1 (Statistics 1)
Year2020
SessionNovember
TopicTree Diagrams
TypeMarkov chain weather transitions

4 In a certain country, the weather each day is classified as fine or rainy. The probability that a fine day is followed by a fine day is 0.75 and the probability that a rainy day is followed by a fine day is 0.4 . The probability that it is fine on 1 April is 0.8 . The tree diagram below shows the possibilities for the weather on 1 April and 2 April.
  1. Complete the tree diagram to show the probabilities. 1 April
    \includegraphics[max width=\textwidth, alt={}, center]{33c0bd01-f27b-424c-a78a-6f36178bc08c-08_601_405_706_408} 2 April Fine Rainy Fine Rainy
  2. Find the probability that 2 April is fine.
    Let \(X\) be the event that 1 April is fine and \(Y\) be the event that 3 April is rainy.
  3. Find the value of \(\mathrm { P } ( X \cap Y )\).
  4. Find the probability that 1 April is fine given that 3 April is rainy.