The ratio of boys to girls in mr castello's class is 2 to 3 which of the following cannot be the total number of students in mr castello's class 20 24 25 30

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.

Bis your answer. it only holds the decimal numerals