CAIE S1 2018 November — Question 3

Exam BoardCAIE
ModuleS1 (Statistics 1)
Year2018
SessionNovember
TopicTree Diagrams
TypeSequential selection without replacement

3 A box contains 3 red balls and 5 blue balls. One ball is taken at random from the box and not replaced. A yellow ball is then put into the box. A second ball is now taken at random from the box.
  1. Complete the tree diagram to show all the outcomes and the probability for each branch. First ball
    Second ball
    \includegraphics[max width=\textwidth, alt={}, center]{7dc85f33-2647-4f73-8093-524b70f99767-04_655_392_688_474}
    \includegraphics[max width=\textwidth, alt={}, center]{7dc85f33-2647-4f73-8093-524b70f99767-04_785_387_703_1110}
  2. Find the probability that the two balls taken are the same colour.
  3. Find the probability that the first ball taken is red, given that the second ball taken is blue.