#### Answer

See examples below.

#### Work Step by Step

We provide examples of writing fractions as percents and percents as fractions:
Fraction as percent:
To convert $\frac{1}{2}$ to a percent, set up a proportion with $\frac{p}{100}$:
$\frac{1}{2}=\frac{p}{100}$
Then cross-multiply:
$1*100=p*2$
And solve for $p$:
$p=100/2=50$
Thus $\frac{1}{2}$ as a percent is $50\%$.
Percent as fraction:
To convert $40\%$ to a fraction, write it as a fraction with 100 in the denominator:
$40\%=\frac{40}{100}$
Next, simplify the fraction:
$\frac{40}{100}=\frac{20}{50}=\frac{2}{5}$
Thus $40\%$ as a fraction is $\frac{2}{5}$.
(Alternatively, one can use the table at the end of this section to convert common percents/fractions.)