Unit 2

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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...

EXAMPLE:

Increase 240 by 25%:

1. 25 % = 0.25

2.0.25 becomes 1.25

3. 1.25 * 240 = 300

CORBETTMATHS REFERENCE : VIDEO 238

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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 

EXAMPLE

Decrease 160 by 30%

1.30%= 0.3

2.  1.00-0.3 = 0.7

3. 160 * 0.7 = 112

CORBETTMATHS VIDEO REFERENCE : 238

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Compound Interest

Compound interest is when a multiplier is used repetitively to work out a value over time.

FORMULA: original amount * multiplier^amount of years 

EXAMPLE

£1000 is put into an account with 5% interest. How much is the account after 3 years?

1000 * 1.05^3 = £1157.63 

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Reverse Percentages

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:

x= 32/0.4

x=80

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