In a warehouse, a dozen eggs and 10 apples had the same price. After a week, the price of eggs dropped by $2 \%$ and the price of apples increased by $10 \%$. How much more will be spent on the purchase of a dozen eggs and 10 apples?
(a) $2 \%$
(b) $4 \%$
(c) $10 \%$
(d) $12 \%$
(e) $12.2 \%$
The correct option is (b).

Since the statement and the answer are in percentages, we can, in this case, set any price and any currency unit, and the answer will always be the same. The simplest approach, therefore, is to assume that initially, a dozen eggs cost 100 and that 10 apples also cost 100. Since the price of eggs increased by 10%, the new price of eggs is 110. The price of apples decreased by 2%, so the new price of 10 apples is 98. Thus, while it used to cost 200 to buy a dozen eggs and 10 apples, it now costs $110+98=208$. Therefore, the increase was 8 out of 200, which corresponds to the percentage of

$$
\frac{8}{200}=\frac{4}{100}=4 \%
$$