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# Percentage Growth and Decay

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by

## Mr Mattock

on 13 September 2018

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#### Transcript of Percentage Growth and Decay

Percentage Growth and Decay
Starter
Starting with 100%, what percentage do you have if the original is:

(a) increased by 20%?
(b) decreased by 20%?
(c) increased by 2%?
(d) decreased by 2%?
(e) increased by 0.2%?
(f) decreased by 0.2%?
Activity
Complete the percentage growth and decay worksheet.
Percentage growth and decay
The value of a car depreciates by 20% every year. If the car is £39999 brand new, work out the value of the car after 5 years.
L.O. - To calculate growth and decay given as a percentage change.
Starter
Starting with 100%, what percentage do you have if the original is:

(a) increased by 20%?
120%
(b) decreased by 20%?
80%
(c) increased by 2%?
102%
(d) decreased by 2%?
98%
(e) increased by 0.2%?
100.2%
(f) decreased by 0.2%?
99.8%
Percentage growth and decay
The value of a car depreciates by 20% every year. If the car is £39999 brand new, work out the value of the car after 5 years.
39999 x 0.8 = £13106.87
5
Percentage growth and decay
The value of an antique increases by 4.6% every 5 years. Work out the total percentage increase of the antique over 100 years.
Percentage growth and decay
The value of an antique increases by 4.6% every 5 years. Work out the total percentage increase of the antique over 100 years.
100 x 1.046 = 245.83% of original so
145.83% increase.
20
Activity
Complete the percentage growth and decay worksheet.
1) \$160.12
2) 43872 people
3) \$361223.09
4) 500 x 0.88
2.37 x 10 mL

5) 51.2 mg
6) Approx 1.8 years
7) Approx 19 hours
8) Approx 29 days
n
-11
Plenary
Toby wants to buy a car.
A new car costs £15 450.
A different make of car that is two years old costs £10 500.
Each car depreciates in value by 20% per year.
He plans to sell the car when it is 7 years old.
Which car would be worth the most when he sells it?

Plenary
Toby wants to buy a car.
A new car costs £15 450.
A different make of car that is two years old costs £10 500.
Each car depreciates in value by 20% per year.
He plans to sell the car when it is 7 years old.
Which car would be worth the most when he sells it?
New car - 15450 x 0.8 = £3240.10
Used car - 10500 x 0.8 = £3440.64
Used car worth more.
7
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Activities
Activity

Key
Examples

Worked
Example

Worked
Example

Bright Spark:
You have two vouchers for a restaurant, one that gives you 10% off, and one that gives you 20% off. Which order should you use them?

What about if the 20% off is only on the main course?
Full transcript