Writing one number as a percentage of another

To write one number as a percentage of another, divide the first number by the second number, then multiply by 100.
Dress with 10% off tag

a) A dress which originally cost \pounds{80} is reduced by \pounds{10} in the sale. What percentage reduction is this?

b) A swimming team has {20} members and {12} of these are boys. What percentage of the swimming team are boys?

a) 10 \div 80 = 0.125

0.125 \times 100\% = 12.5\%

So the dress has been reduced by 12.5\%.

b) \frac{12}{20} \times 100 = 60

So 60\% of the team are boys.