Priti owns two bags of discs, $X$ and $Y$. Bag $X$ has 8 red discs and 7 blue discs, while bag $Y$ has 6 red discs and 9 blue discs. Priti throws a fair coin. If the result is a head, she randomly selects two discs from bag $X$ without replacement. If the result is a tail, she randomly selects two discs from bag $Y$ with replacement.
(a)[2]
Draw a tree diagram to show the information, including all probabilities.
(b)[2]
Find the probability that the two discs Priti chooses are blue.
(c)[4]
Find the probability that the two discs Priti chooses come from bag $X$ given that at least one disc is red.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Tree diagram showing all 2, 4, 8 branches; labels H, T, R, B and at least 4 correct probabilities” …