There’s a few things you might be asked to do with percentages….
Find X% of Y
Just turn the percentage into a decimal then multiply.
So 30% of £80 = 0.3 x £80 = £24
What Is The Amount After An X% Increase / Decrease?
E.g. A car’s price is reduced by 45%. It originally cost £80. What does it cost now?
Write 45% as a decimal and multiply by £80 to find the change in price.
0.45 x £80 = £36.
Therefore you know it was reduced by 36 quid. So the new cost is:
£80 – £36 = £44
Express X As A Percentage Of Y
E.g. Express 76p as a percentage of £2.34.
Make sure the figures are in the same units – so here put them both in pence.
Then just divide 76p by 234p and multiply by 100:
(76/234) x 100 = 32.48%
Find The Percentage ChangeSo if you buy an apple (a classic maths problem situation) for 20p and sell it for 30p your percentage profit is:
(30-20)/20 x 100 = 50%
Finding The Original Value
These can be tricky to recognise…but if you have to work out the original amount then don’t panic and follow this method:
- write the new amount as a percentage of the original
- divide by whatever this percentage is to find 1% of the original
- Multiply by 100 to get the original
So if a car goes up in price by 20% and is now £7,200 to find the original amount you have to:
- Realise that £7,200 is 120% of the original
- Divide £7,200 by 120 to get 1% of the original
- Multiply by 100
So original price = (£7,200/120) x 100 = £6000