Exam-Style Question on Probability
A mathematics exam-style question with a worked solution that can be revealed gradually
Question id: 11. This question is similar to one that appeared on an IB Studies paper in 2010. The use of a calculator is allowed.
Julie chooses a cake from a yellow box on a shelf. The box contains two chocolate cakes and three plain cakes. She eats the cake and chooses another one from the box. The tree diagram below represents the situation with the four possible outcomes where C stands for chocolate cake and P for plain cake.
(a) Write down the value of \(x\).
(b) Write down the value of \(y\).
(c) Find the probability that both cakes are plain.
On another shelf there are two boxes, one red and one green. The red box contains four chocolate cakes and five plain cakes and the green box contains three chocolate cakes and four plain cakes. Ben randomly chooses either the red or the green box and randomly selects a cake.
(d) Copy and complete the tree diagram below.
(e) Find the probability that he chooses a chocolate cake.
(f) Find the probability that he chooses a cake from the red box given that it is a chocolate cake.
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