Calculating percentages
You need to be able to use basic skills of working with percentages for many different calculations. Percentages are often used for:
- prices and sales
- saving and borrowing money
- test scores
Most questions about percentages will be in a real life context.
Per cent means 'out of one hundred', so \(15\%\) means \(15\) out of \(100\).
\(15\% = \frac{{15}}{{100}}\)
Example
Calculate \(15\%\) of \(\pounds200\)
Answer
\(\frac{15}{100}\times 200= \pounds30\)
Now try the example questions below.
Question
Find \(30\%\) of \(\pounds800\).
\(30\%\) of \(\pounds800\)
=\(\frac{30}{100}\times 800\)
\(= \pounds240\)
Calculate percentages with a calculator
You can use a calculator to work out percentages in just the same way as you you worked with fractions. Just remember that a percentage is the same as a fraction of one hundred.
For exammple \(15%\) means the same as \(\frac{15}{100}\).
To work out \(15%\) of \(924\) on a calculator, you could enter any of the following:
\(15 \div 100 \times 924\)
\(924 \div 100 \times 15\)
\(924 \times 15 \div 100\)
Each gives the same answer of \(138.6\)
Answer the following, either on paper or using a calculator.
Question
Find \(17\%\) of \(340kg\)
\(17\%\) of \(340kg\)
= \(\frac{17}{100}\times 340\)
A way of doing this on a calculator is \(340 \div 100 \times 17\).
\(=57.8kg\)
Question
Find \(15\%\) of \(260cm\)
\(15\%\) of \(260cm\)
= \(\frac{15}{100}\times 260\)
One way of doing this on a calculator is \(260\div 100\times 15\).
\(=39cm\)