Paper 1 · probability / tree diagrams

An ice cream vendor's sales are 40% chocolate, 35% vanilla and 25% peach. The probability of a cone sale is 0.80 for chocolate, 0.60 for vanilla and 0.40 for peach. What is the overall probability that a randomly selected sale is by cone?

A0.60

B0.58

C0.63

D0.67

Explanation: By the law of total probability,

P(\text{cone}) = 0.40(0.80) + 0.35(0.60) + 0.25(0.40) = 0.32 + 0.21 + 0.10 = 0.63

Derived from ZIMSEC Statistics Paper 1, November 2021, Q2

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