Please help...

Question

The ratio of the number of boys to that of girls in Class A is 2 : 3. The ratio of the number of girls who wear glasses to the number of girls who do not wear glassesis 1:3. If there are 12 more girls than boys, how many girls wear glasses?

Answer 1

let the number of boys be 2x
let the number of girls be 3x
(notice boys:girls = 2x:3x = 2:3 )

given: 3x - 2x = 12
x = 12

so we know there were 24 boys and 36 girls

let the number of girls who wear glasses be y
let the number of girls who don't wear glasses be 3y

y + 3y = 36
4y = 36
y = 9

So 9 girls wear glasses