9) In a school, $60 \%$ of the students are male, $90 \%$ are minors, and $60 \%$ have brown hair. Which of the following statements is necessarily true?

(A) There is at least one female who is of age.

(B) There is at least one female with brown hair.

(C) There is at least one minor male with brown hair.

(D) There are no males of age with brown hair.

(E) There is at least one blonde male.
9) The answer is (C)

The girls are $40 \%$, the non-brown-haired $40 \%$, and the adults $10 \%$. Even if there were no overlap, the total would reach $90 \%$, leaving $10 \%$ for male minors with brown hair. On the other hand, statements (A), (B), (D), and (E) can be false, as can be seen from the following example of a school with 1000 students:

if in the school there are 400 girls, all minors and blonde, and 600 boys all with brown hair, of which 500 minors and 100 adults, all the statements in the text are true, but (A), (B), (D), (E) are false.