Ali ate half of a muffin. What percentage of the muffin did Ali eat?
(A) $10 \%$
(B) $17 \%$
(C) $21 \%$
(D) $40 \%$
(E) $50 \%$
As a percentage, one half of a muffin is equivalent to $\frac{1}{2} \times 100 \%=50 \%$ of a muffin.

ANSWER: (E)