Using the same school (55% own O-level pupils, 45% from elsewhere; pass rates 70% and 90% respectively, overall pass probability 0.79), given that a graduate passed A-level, what is the probability that they did O-level outside the school?

A0.45

B0.487

C0.513

D0.90

Explanation

By Bayes' theorem,

P(\text{outside}|\text{pass}) = P(\text{pass}|\text{outside})P(\text{outside})/P(\text{pass}) = (0.90\times0.45)/0.79 = 0.405/0.79 \approx 0.513

Derived from ZIMSEC Maths Paper 1, November 2008, Q2 (Statistics)

More questions from this paper

Danho has every sitting for this paper, with your progress tracked question by question, offline.