[Inequality problems. Case analysis]

In a certain school, a council of 5 students was elected in each of the 20 classes. Petya turned out to be the only boy elected to the council along with four girls. He noticed that in 15 other classes, more girls were elected than boys, although in total, the number of boys and girls elected in the school was equal. How many boys and how many girls are in the councils of the four remaining classes (in total)?
In total, 5$\cdot$20 = 100 people were selected to the council. Half of them are girls, which is 50. If more girls were selected from a class than boys, then at least three girls were selected. Therefore, in 15 classes, at least 45 girls were selected. Four more girls were selected from Petya's class. Since Petya is the only boy who ended up in the council along with four girls, no more than three girls could have been selected in any other class. Therefore, in 16 classes, exactly 49 girls were selected. Consequently, in the remaining four classes, 19 boys and one girl were selected.

## Answer

19 boys and one girl.