Appendix G
PERCENTAGES
What is A Percentage?
Percentages are important. We are always meeting up with them whether we like them or not.
Percentages are used in most sporting competitions. The percent sign looks like this: %.
Stores offer sales with 20% off. Taxes are quoted in percentages. We are told there is a 6% surcharge
on certain items. Most people are happy to let somebody else calculate the amount for them, and they
simply take the person’s word for what they pay.
Often we need to calculate what we will have to pay beforehand — we need to be able to calculate
percentages for ourselves.
Percentages are really fractions: ‘percent’ actually means ‘for every hundred’. So 50% means 50 for
every 100, or ^50 / 100 . You can see that 50 and 100 are both divisible by 50. Fifty divides once into 50 and
twice into 100. So 50% is the same as ^50 / 100 or ½. It makes sense that 50 is half of 100.
If you read that 23% of people have blond hair, it means that 23 people out of every 100 have blond
hair. You could also say that 0.23 of the population has blond hair, but it is easier and more common to
say it as a percentage.
Money has built-in percentages. Because there are 100 cents in a dollar, 54 cents is 54% of a dollar.
Calculating A Quantity As A Percentage of Another
How do you find what percentage one number is of another? For instance, if 32 people at a meeting are
females and there are 58 people attending, what percentage are female? As a fraction they are ^32 / 58 . To
find the percentage you simply multiply this by 100.
You calculate this as follows:
(^32) /
58 (100 =
3,200/
58 %
3,200 ÷ 58 = 55^10 / 58 %
This would normally be expressed as a decimal: 55.17%.
So, 25 boys in a crowd of 50 would mean that 50% are boys. Why? Because half are boys and ½
times 100 is 50. We simply multiply the fraction by 100.
On the other hand, to find a percentage of a number — for instance, what is 20% of 2,500 — we
multiply the number by the percentage divided by 100. We would set it out like this:
2,500 × ^20 / 100 =
We can cancel the one hundreds, or simply divide 2,500 by 100, which is, of course, 25. Then
multiply 25 by 20 (multiply by 2, then by 10) to get 500.
So, summarised, to calculate the percentage of 17 to 58, for example, you would divide 17 by 58 and
multiply the answer by 100. Your calculation would look like this:
(^17) /
58 × 100 =