There are 21 pupils who study Maths, 29 pupils who study french, 26 pupils who study history. there are 4 pupils who study both maths and french. 10 pupils who study both french and history and 3 pupils who study both maths and history. there 1 pupil who studies all three subjects.

two different pupils are selected at random. find the probability that they both study history.

Help, i do not understand this question.

1 answer

If we consider the selections as independent events, then since there are

(21+29+26)-(4+10+3)+(1) = 60

students, of whom 26 study history, the chance of any student's studying history is 13/30.

So, the chance of both is (13/30)^2