The ratio boys to girls is 5/4. If a few boys leave the class, the ratio boys to would become the reciprocal of the earlier ratio. Which of the following CANNOT be the possible number of boys and girls in the class?
a) 45
b) 90
c) 120
d) 135
I know we have 9 parts, but what to do next?
The impossible answer is $120$
Boys ratio and girls ratio are $\frac{5}{9}$and $\frac{4}{9}$, respectively
Any of these two fractions of $120$ are not an integer.