There are 720 boys and 700 girls in a school. The probability that a boy chosen at random studies French is 2/3 The probability that a girl chosen at random studies French is 3/5. Work out the number of students in the school who study French.

Let x denote the number of boys studying French and y the number of girls studying French. Then the probability that a boy chosen random studies French is x/720 and the probability that a randomly chosen girl studies French is y/700.As x/720=2/3 it follows that x=7202/3=480, the number of boys studying French. Similarly, as y/700=3/5, y=3/5700=420, the number of girls studying French. Therefore, there are 420+480=900 students studying French in this school.