Calculating percentages of amounts
In a nutshell
It is often useful to calculate percentages of amounts when solving problems. Some are simple and some require a little more work.
Finding percentages of amounts
There are two methods to calculating percentages of amounts: by using simple percentages that you already know, or by converting the percentage to a fraction and multiplying.
Method 1: Using simple percentages
You can always split up a percentage into smaller simple ones. Below are some simple percentages that you need to remember how to calculate, as well as their equivalent fraction pairs.
PERCENTAGE  FRACTION  HOW TO CALCULATE 
$50 \%$
 $\frac{1}{2}$
 Divide by two

$25\%$
 $\frac{1}{4}$
 Divide by four

$10\%$
 $\frac{1}{10}$
 Divide by ten

$5\%$
 $\frac{1}{20}$
 Divide by ten and then two

$1\%$
 $\frac{1}{100}$
 Divide by one hundred

Example 1
In a sale, everything is $17\%$ off. What saving would be made on $£200$?
Split $17\%$ into simple percentages.
$17\%=10\%+5\%+1\%+1\%$
Work out each of the simple percentages.
$10\%$ of $200 = 200\div10=20$
$5\%$ of $200= 10\% \div 2=20\div2=10$
$1\%$ of $200= 200\div100=2$
Add together the simple percentages.
$20+10+2+2=\underline{£32}$
Method 2: Turn into a fraction and multiply
The second method is to simply turn the percentage into a fraction and multiply by the amount. Remember that to convert from a percentage to a fraction you take the percentage as a fraction out of one hundred.
Example 2
Calculate $29\%$ of $£3300$.
Write $29\%$ as a fraction out of one hundred.
$\frac{29}{100}$
Multiply by $£3300$.
$\begin{aligned}\frac{29}{100}\times£3300=£3300 \div 100 \times 29\\=£33 \times 29 = \underline{£957} \end{aligned}$