Question 1180192
x is total number of children
(2/5)x are 13, and 3/4 of them or (3/10)x altogether are girls
(3/5)x are 14, and we know that (2/10)x or (1/5)x of them are girls to make them 50% of all the students. 3/5*x=2/10 or 1/5. That means 1/3 of the 14 year-olds are girls (because (3/5)(1/3)=1/5, so 2/3 of the 14 year-olds are boys.

Can check assuming 120 in class, 60 boys and 60 girls
48 are 13 and 72 are 14
36 are girls 13, so 24 girls have to be 14.
24 is 1/3 of 72, so the boys are 2/3 of the 14 year-olds.