Increase By A Percentage
Using multipliers to increase a number by a percentage.
To increase a number by a percentage:
1.Change the percentage you're going to increase the number by into a decimal
2. Put a 1 before the decimal to make it 1 point something (look at example below)
3. Multiply the number that you have been told to increase by the decimal with 1 point...
Increase 240 by 25%:
1. 25 % = 0.25
2.0.25 becomes 1.25
3. 1.25 * 240 = 300
CORBETTMATHS REFERENCE : VIDEO 238
Decrease By A Percentage
Using Multipliers to decrease a number by a percentage
To decrease a number by a percentage :
1.Change the percentage given into a decimal
2. Take that decimal away from 1.00
3. Multiply the decimal with the number told to decrease
Decrease 160 by 30%
2. 1.00-0.3 = 0.7
3. 160 * 0.7 = 112
CORBETTMATHS VIDEO REFERENCE : 238
Compound interest is when a multiplier is used repetitively to work out a value over time.
FORMULA: original amount * multiplier^amount of years
£1000 is put into an account with 5% interest. How much is the account after 3 years?
1000 * 1.05^3 = £1157.63
How to work out an original amount following a percentage change
For a percentage change to happen, a multiplication needs to take place. For example :
40 % of a number is 32. What is the original number?
This means x (which is the original number) multiplied by 0.4 (multiplier for 40 %) is equal to 32
x * 0.4 = 32
Then, just rearrange the above equation to find x: