Calculate percentages using the fraction method
To write one number as a percentage of another, divide the first number by the second number to make a fraction, then multiply by 100.
Example
\(15\) out of \(30\) pupils in a class are girls. Express this as a percentage.
Answer
\(\frac{{15}}{{30}} \times 100 = 50\%\)
\(50\%\) of the class are girls.
Question
A dress which originally cost \(\pounds{80}\) is reduced by \(\pounds{10}\) in the sale. What percentage reduction is this?
\(10 \div 80 = 0.125\)
\(0.125 \times 100\% = 12.5\%\)
So the dress has been reduced by \(12.5\%\).
Question
A swimming team has \({20}\) members and \({12}\) of these are boys. What percentage of the swimming team are boys?
\(\frac{12}{20} \times 100 = 60\)
So \(60\%\) of the team are boys.
Question
A new healthy snack bar called 'Fibre-crunch' is being sold in the shops.
Each bar weighs \(40g\) and contains \(2g\) of protein, \(3g\) of fat and \(35g\) of carbohydrate.
What percentage of protein, fat and carbohydrate does 'Fibre-crunch' contain?
Percentage of protein:
\(= \frac{2}{{40}} \times 100 = 5\%\)
Percentage of fat:
\(= \frac{3}{{40}} \times 100 = 7.5\%\)
Percentage of carbohydrate:
\(= \frac{{35}}{{40}} \times 100 = 87.5\%\)
