If the price of a product increased from $R \$ 5.00$ to $R \$ 5.55$, what was the percentage increase?
The increase in reais was $5.55-5=0.55$; so the percentage increase was

$$
\frac{0.55}{5}=\frac{0.55 \times 20}{5 \times 20}=\frac{11}{100}=11 \%
$$