7.1. $\quad$ In the 7a class, $60 \%$ of the students are girls. When two boys and one girl were absent due to illness, the percentage of girls present was $62.5 \%$. How many girls and boys are there in the class according to the list?
Answer: 21 girls and 14 boys. Solution. Let there be $d$ girls and $m$ boys in the class. From the conditions of the problem, we have two equations: $\frac{d}{d+m}=0.6$ and $\frac{d-1}{d+m-3}=0.625$. From the first equation, $2 d=3 m$. Substituting $m=\frac{2}{3} d$ into the second equation and solving it, we get $d=21$, and then $m=14$.