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Level 5-6 Numbers - Percentages - Increases and Decreases
A train's top speed is 140 mph. Find out more in this quiz.

Level 5-6 Numbers - Percentages - Increases and Decreases

Percentages help track change. Learn how increases and decreases work, and why repeated percentage changes use multiplication, not simple addition.

Fascinating Fact:

Compound changes multiply repeatedly, two 10 percent rises are not 20 percent total, but 1.10 × 1.10 = 1.21, a 21 percent increase.

In KS3 Maths, you study percentage increases and decreases to model real price changes, discounts, and growth. Using multipliers (like 1.2 or 0.85) keeps calculations fast and accurate.

  • Percentage: A fraction out of 100, written with the percent symbol (%).
  • Multiplier: The number you multiply by to apply a percentage change, for example 1.08 for an 8% increase.
  • Compound change: Repeated percentage change where each step builds on the last using multiplication.
How do you increase a number by a percentage in KS3?

Convert the percentage to a multiplier and multiply. For example, increase 250 by 12% using 250 × 1.12 = 280.

How do you decrease a number by a percentage?

Use a multiplier less than 1. A 15% decrease uses 0.85. Example: 60 × 0.85 = 51.

Why are two 10% increases not equal to a single 20% increase?

Because the second 10% is on the new value. 1.10 × 1.10 = 1.21, which is a 21% total increase, not 20%.

1 .
Harold owns a 14% stake in a company worth £250,000. How much is Harold's stake worth?
£35,000
£40,000
£45,000
£50,000
To find 14% multiply by 0.14
2 .
The local football team are playing badly and the number of season tickets sold reduces by 17% from last year. If 3,700 tickets were sold last year, how many were sold this year?
3,000
3,071
3,091
3,099
To find 17% multiply by 0.17
3 .
Thomas earns £22,500 per year. He receives a pay rise of 4.4%. How much does he now earn?
£23,000
£23,400
£23,450
£23,490
4.4% of 22,500 is 990. To work this out you could multiply 22,500 x 0.044 (4.4 hundredths)
4 .
To find the result of increasing a number by 66% you multiply it by .......
1.16
1.6
1.66
34
Calculations are much easier if a multiplier is used
5 .
To find the result of increasing a number by 13% you multiply it by .......
1.13
1.3
1.31
87
If something is increased by x% then its original value will have to be multiplied by (1 + x) to find the new value. The 1 represents 100% and the x represents the percentage increase: in this case (1 + x) = (1 + 0.13) = 1.13. If there was a decrease of x%, then you would have to multiply the original value by (1 - x)
6 .
To find the result of decreasing a number by 7% you multiply it by .......
0.9
0.93
1.07
1.7
Percentages are easily converted to decimals. Just divide by 100 (or move digits)
7 .
A train's top speed is 140 mph. After a service, its top speed increases by 12%. What is the new top speed?
150 mph
156 mph
156.4 mph
156.8 mph
A 12% increase is a multiplier of 1.12. 1.12 x 140 = 156.8
8 .
Simon bought his computer for £230. A year later he sold it for 20% less than he paid for it. How much was it sold for?
£164
£184
£204
£224
To work out 20% just divide by 5
9 .
In a sale, all the prices are reduced by 20%. Find the sale price of a washing machine which originally cost £299.
£60
£100
£176.30
£239.20
One way is 20 / 100 x £299 = £59.80. Then subtract £59.80 from £299 to get £239.20
10 .
Bob, the local car dealer, is reducing all his cars by 15%. Find the reduced price of a Nissan which originally cost £690.
£580.60
£585.50
£586.50
£590.90
Another way is to use a multiplier. A 15% decrease is a mutliplier of 100 - 15 = 85%. 85% = 0.85 (just divide 85 by 100). £690 x 0.85 = £586.50
You can find more about this topic by visiting BBC Bitesize - Percentages

Author:  Frank Evans (Specialist 11 Plus Teacher and Tutor)

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