11) A batch of watermelons initially weighing $500 \mathrm{~kg}$ is stored for a week in a warehouse. At the beginning, the percentage of water contained in the watermelons is $99 \%$ of their weight, at the end of storage, due to evaporation, this percentage has dropped to $98 \%$. How much do the watermelons weigh at the end?
(A) $250 \mathrm{~kg}$
(B) $400 \mathrm{~kg}$
(C) $480 \mathrm{~kg}$
(D) $490 \mathrm{~kg}$
(E) $495 \mathrm{~kg}$.
11) The answer is $\mathbf{( A )}$.

The non-aqueous component of the watermelons initially constitutes $1 \%$ of the total weight, and thus is $5 \mathrm{~kg}$. At the end of storage, these $5 \mathrm{~kg}$ represent $2 \%$ of the total weight, which is therefore $\frac{5 \cdot 100}{2}=250 \mathrm{~kg}$.