Paper 2 · probability
Whenever there is a power-cut, a school is equally likely (probability 1/3 each) to switch on one of its 3 generators A, B or C. The independent probabilities of a breakdown are 0.2 for A, 0.3 for B and 0.25 for C. For a randomly chosen day with a power-cut, what is the probability that there was a generator breakdown?
A0.20
B0.30
C0.25
D0.75
Explanation: By the law of total probability, P(breakdown) = (1/3)(0.2) + (1/3)(0.3) + (1/3)(0.25) = (0.2+0.3+0.25)/3 = 0.75/3 = 0.25.
Derived from ZIMSEC Statistics Paper 2, November 2018, Q3
