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# Percentage Change

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by

## Mr Mattock

on 28 November 2015

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#### Transcript of Percentage Change

Percentage Change
Examples
L.O. - Use multipliers to calculate the result of percentage changes (Grades 4 to 7)
The value of machinery in a factory
depreciates by 20% each year. The
machinery was bought for £74,500.

James says, "20% of £74500 is £14900, so after 2 years, the price of the machinery will have fallen by £29800."

The polar ice cap in the Arctic is 4 metres
thick. If the ice is thinning at a rate of 6% per
year, how thick will the ice be in 5 years time?
£14,000 is invested at 9.25% per annum compound interest. Find the total amount at
the end of 3 years.
The value of machinery in a factory depreciates by 20% each year. The machinery was bought for £74,500.

James says, "20% of £74500 is £14900, so after 2 years, the price of the machinery will have fallen by £29800."

No, because after the first year, 20% will no longer be £14900.
Starter
Teachers wages rise by 1% each year. The starting salary for a teacher is £22,244.
(a) How much will it be next year?

(b) Most teachers go up a point on the pay scales after 1 year. This represents a rise of 7.9% on the starting salary. Taking into account that this too will be subject to a 1% increase, work out pay for a second year teacher next year.
Teachers wages rise by 1% each year. The starting salary for a teacher is £22,244.
(a) How much will it be next year?
£22244 x 1.01 = £22,466

(b) Most teachers go up a point on the pay scales after 1 year. This represents a rise of 7.903% on the starting salary. Taking into account that this too will be subject to a 1% increase, work out pay for a second year teacher next year.
Either £22466 x 1.07903 or £22244 x 1.07903 x 1.01 = £24242
£14,000 is invested at 9.25% per annum compound interest. Find the total amount at
the end of 3 years.

£14000 x 1.0925 = £18255
The polar ice cap in the Arctic is 4 metres
thick. If the ice is thinning at a rate of 6% per
year, how thick will the ice be in 5 years time?

4 x 0.94 = 2.94 metres.
3
5
Examples
£308.70
£357.36
30565
6 years
Main Activity
Complete the percentage change
sheet.
Main Activity
£1375

(a) £1272
(b) £1348.32
(c) £1605.87

(a) £8144.47
(b) £7990.66
(c) £10021.16

C (£51.94)
£227.29

(a) £900
(b) £284.77
(c) £90.10

£4608

(a) 6 years
(b) (i) 5 years
(ii) 8 years
£94.50

£1.78

(a) 45,229,406
(b) 8 years
(a) (i) £3,132
(ii) 52.2%
(b) (i) £6,264
(ii) 52.2%
(c) Same % reduction

(a) £180
(b) £571.31
Plenary
An item undergoes successive percentage changes of 90%, then 80%, then 70%, and so on until a final change of 10%.

(a) If the changes are increases, calculate the total percentage increase.

(b) If the changes are decreases, calculate the total percentage decrease.
Plenary
An item undergoes successive percentage changes of 90%, then 80%, then 70%, and so on until a final change of 10%.

(a) If the changes are increases, calculate the total percentage increase.
3352%

(b) If the changes are decreases, calculate the total percentage decrease.
99.96%
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