Maths
Percentages
'Percent' means 'per 100'. If 70 percent of the population own a pet, this means that 70 out of every hundred people own a pet. The symbol '%' means 'percent'.
This Revision Bite covers:
In this diagram, 30 out of 100 squares have been shaded. So 30% has been shaded.
It's often useful to be able to find a percentage of a quantity. For example, you might be told that bus fares are going up by 5% and you need to know how much more you will need each week.
Here are a couple of ways you could do it:
Find 1% of the quantity by dividing it by 100.
Find x% of a quantity by multiplying 1% of the quantity by x.
Rakesh has a box containing 60 pens. 20% of the pens are red. How many is that?
You need to find 20% of 60.
1% of 60 is 60 ÷ 100 = 0.6
So 20% of 60 is 0.6 × 20 = 12
Find x% of a quantity by multiplying that quantity by x/100
This combines the division and multiplication of Method 1 into one sum.
Q1. In a class of 25 pupils, 24% live in a flat. How many pupils live in a flat?
Q2. Last year Sam earned £20,000. This year her pay has increased by 8%.
a) By how much money has Sam's pay increased?
b) What is her new salary?
A1. 24% is equivalent to 24/100
24% of 25 = 24/100 × 25 = 6
Therefore 6 pupils live in a flat.
A2.
a) Method 1:
1% of 20000 = 20000 ÷ 100 = 200
8% of 20000 = 8 × 200 = 1600.
Method 2:
8/100 × 20000 = 1600.
b)Therefore, her new salary is:
£20000 + £1600 = £21600.
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