Question

Suppose the ratio of boys to girls in a school of 720 students is 7 : 5. How many more girls should be admitted to make the ratio 1 : 1?

Answer 1

For every $7$ boys there are $5$ girls. Thus out of $12$ students, $7$ are boys and $5$ are girls. Hence the number of boys is
$\frac{7}{12}\times 720=420$.
The number of girls is$720-420=300$. Now we want the ratio of boys to girls to be $1:1$. This means the number of boys and girls must be same. Since the deficiency of girls is $420-300=120$, the school must admit 120 girls to make the ratio $1:1$.