Percentages
Finding easy percentage of…
Remember 10% means
so to find 10% just divide by 10
eg. 10% of £250
so to find 20% or 30% etc:
·
Find 10%
· Multiply by 2 for 20%
3 for 30% etc
eg. 30% of £370
10% of £370 (move decimal point one place to the
left)
so, 30%
of £370
Percentage of… (eg. 21% of £350)
· Write the percentage as a fraction over 100
eg.
· Multiply by the number
·
eg. 24% of £300
eg. 24% of £340 (use calculator)
Making Percentages
· Write the amount and total as a fraction:-
· Multiply by 100 to turn fraction into a percentage
eg. 2 out of 8 as a percentage
eg. 30 out of 80 as a percentage
Interest / Gain
1. Write percentage as a fraction
2. Multiply by the amount
3. Add the answer to the amount
eg. £250 invested at 12%. Find the total
Total = £250 + £30
= £280
OR
1. Add percentage to 100%
2. Write as a decimal
3. Multiply by the amount
12% added on to 100% = 112%
Loss / Decrease
Same as above but subtract instead of add.
Eg. loss of 24% on £250
Total = £250 - £60
= £190
OR
Take 24% from 100% gives 76%, so:
Percentage Change
eg. percentage loss; percentage gain; percentage increase; percentage decrease; percentage profit etc.
eg. A plant grew from 20cm to 25cm. Find the percentage increase
% increase
Compound Percentage Change
percentage loss; percentage gain etc several times over.
eg. Population of a village starts at 2500 and increases by 7% each year for 10 years.
Adding 7% to 100% gives 107%, so:
Total after 10 years =
=
= 4917.87839…..
= 4918 to the nearest person.
eg. Number of bubbles starts at 143 and decreases by 8% each minute for 20 minutes.
Taking 8% from 100% gives 92%, so:
Total after 20 minutes =
=
= 26.98314…..
= 27 to the nearest bubble
eg. £200 invested gives 5% interest per year for the first 3 years and then 4% loss for the next 2 years.
Adding 5% to 100% gives 105%
Taking 4% from 100% gives 96%, so:
Total after 5 years =
=
= £213.37344
= £213.37 to the nearest penny