The ratio of boys to girls in a graduation class is 5:4. If there are 153 pupils in this class, how many boys are there?

Answer 1

5/9 = x/180

9x = 900

x = 100

Answer 2

boys : girls = 5 : 4 or 5x : 4x

then 5x + 4x = 153
9x = 153
x = 17

5x = 85
4x = 68

there are 85 boys in the class

check:
85+68 = 153 , check!
85 : 68
= 5 : 4, check

Answer 3

Aaarrgghh! My demon dead brain cell pulled up 180 out of nowhere. (shaking head!)

Thanks for rescuing us, Reiny!