At 8:00 a.m., there were 24 cars in a parking lot.

At 9:00 a.m., there were 48 cars in the same parking lot.

What is the percentage increase in number of cars in the parking lot between 8:00 a.m. and 9:00 a.m.?
(A) $20 \%$
(B) $48 \%$
(C) $72 \%$
(D) $100 \%$
(E) $124 \%$
We want to calculate the percentage increase from 24 to 48.

The percentage increase from 24 to 48 is equal to $\frac{48-24}{24} \times 100 \%=1 \times 100 \%=100 \%$.

Alternatively, since 48 is twice 24, then 48 represents an increase of $100 \%$ over 24 .

ANSWER: (D)