In a school 10% of boys are equal to the one fourth of the girls. What is the ratio of the boys and…

$\frac{10}{100}B=\frac14G$ gives $\frac{B}{G}=\frac{1/4}{1/10}=\frac{10}{4}=\frac52$, so boys : girls = 5 : 2. Check: with 50 boys and 20 girls, 10% of the boys is 5, which equals one-fourth of the girls. The ratio 2 : 1 fails: with 40 boys and 20 girls, 10% of the boys is 4, not 5.