In a class, 40% of students are male. Of the male students, 25% play chess. What percent of the entire class is male and plays chess?

Of the whole class, $40\%$ are male, and $25\%$ of those males play chess. Multiply the percents as decimals: $0.40\cdot0.25=0.10$, which is $10\%$ of the class, choice F. For example, in a class of $100$ students there are $40$ males, and $25\%$ of $40$ is $10$. Choice H ($25\%$) is the percent of males who play chess, not of the class. Choice G ($15\%$) is the difference of the percents. Choice J ($65\%$) adds the percents, which would be right only if the groups did not overlap.