a ratio of 2:3, simply means, you divide some "total" by 2+3, or 5, and then to the ratio of "2" section, you give 2 of those quotients, and to the ratio "3" section, you give it 3 of those.
now, let's check for example 20, 20/5 is 4, 4*2 is 8 boys and 4*3 is 12 girls.
let's check 25, 25/5 is 5, so 5*2 is 10 boys, and 5*3 is 15 girls.
let's check 30, 30/5 is 6, so 6*2 is 12 boys, and 6*3 is 18 girls.
so those work. now let's check 24.
24/5 is 4.8, 4.8*2 is 9.6 boys, so 9 boys and 0.6 of another, so we have to chop off an arm or something.
and 4.8*3 or 14.4 girls, so 14 girls and 0.4 of another, so, we have to chop off both legs and arms or thereabouts.
anyhow...so you'd see which one doesn't work and why.
