Learning about

Using Inverse Operations for finding the original price after a percentage

increase or decrease

To find a percentage of a number,

you..

Divide the percent by 100

And multiply by the number

12% of 40 =

12 100

(= 0.12) X 40= 4.8

Notice that 100 changes the % to

a decimal

If you wanted to

increase 40 by 12%

Find 12% of 40

and then add this answer to 40

112% of 40 = 4.8 + 40

112 100 (= 1.12) X 40

= 44.8

Notice that 112 100 changes the % to

a decimal which is 1.12

The increased amountis (100 + 12)%of the original

If you wanted to

decrease £125 by 23%

Find 23% of 125

and then subtract this answer from 125

77 100 (= 0.77) X 125

= £96.25

Notice that 77 100 changes the % to

a decimal which is 0.77

The reduced amountis (100 - 23)%of the original

23 100 x 125 = 28.75

£125 - £28.75 = £96.25

Input Output

40 X 0.12 4.8

40 44.8X 1.12

To increase by a percentage

Input Output

? X 1.12 44.8

Insurance costs have increased by 12% The cost after the increase is £44.80

What was the cost before the increase?

1.12 44.840

It cost£40

before theincrease

Using inverse operations!

Input Output

? X 1.23 88.56

Insurance costs have increased by 23% The cost after the increase is £88.56

1.23 88.5672

It cost£72

before theincrease

Using inverse operations!

What was the cost before the increase?

Input Output

125 X 0.23 28.75

125 X 0.77 96.25

To decrease by a percentage

What is £125 minus £28.75?

Input Output

? X 0.77 96.25

In a sale stock is reduced by 23% The sale price of a suit is £96.25

0.77 96.25125

It cost£125

before thesale

The sale price is (100-23)% of the original price

Using inverse operations!

What was the cost before the increase?

Input Output

? X 0.82 96.25

0.82 96.25117.38

It cost£117.38

before thesale

The sale price is (100-18)% of the original price

Round to 2dp for money!

What was the cost before the increase?

In a sale stock is reduced by 18% The sale price of a suit is £96.25

Using inverse operations!