One of the teachers at a school is chosen at random. The probability that this teacher is female is 3/5. There are 36 male teachers at the school. Work out the total number of teachers at the school.

This is a 3 marks exam question from the 2016 summer exam with the Edexcel board. The topic tested here is probability. We are given that the probability of having a female teacher is 3 out of 5. This means that the probability of having a male teacher is 1 - 3/5= 2/5, this proportion corresponding to the given 36 male teachers. We know that 36 is 2/5 (40%) of the total number of teachers. Hence 10% will be 36/4= 9 teachers, and 100% will be 90 teachers in total.