In a class where there are as many girls as boys, 2/5 of the boys and 1/2 of the girls went to a local fair. What fraction of the students in the class did not go to the local fair?

n boys and n girls so 2 n total

3 n/5 + n/2 did not go

that is 6 n/10 + 5 n/10 = 11 n/10
did not go

11 n/10 / 2n = (11/20) did not go