If 40% of a class are girls, and 25% of girls play tennis, what percent of the class play tennis?

A 10%

explanation

Percent of class playing tennis = (Percent of girls in class) × (Percent of girls playing tennis).
Substituting the given values into this equation, we get:
Percent of class playing tennis = 0.40 × 0.25 = 0.10
Therefore, 10% of the class plays tennis.