Percentage decrease with a multiplier

The Maths Habit

A coat has 20% off.
Sam says: "So I pay 20% of the price."
Is Sam right?

100% = the price−20%80%: what Sam pays
No. 20% comes off. Sam pays what is left: 80%.

Decrease
To make smaller.
100% = the amount−20%
Multiplier
The number you multiply by.
amount× multipliernew amount

Type it into your calculator. What does it show?

80÷100=0.8
65÷100=0.65
95÷100=0.95

Find the multiplier to decrease by 20%.

100% = the amount−20%80%
100%−20%=80%
80÷100=0.8multiplier

Find the multiplier to decrease by 30%.

100% = the amount−30%70%
100%−30%=70%
70÷100=0.7multiplier

Find the multiplier to decrease by 20%.

100% = the amount−20%80%
100%−20%=80%
80÷100=0.8multiplier

Find the multiplier to decrease by 15%.

100% = the amount−15%85%
100%−15%=85%
85÷100=0.85multiplier

Find the multiplier to decrease by 20%.

100% = the amount−20%80%
100%−20%=80%
80÷100=0.8multiplier

Find the multiplier to decrease by 60%.

100% = the amount−60%40%
100%−60%=40%
40÷100=0.4multiplier

Find the multiplier to decrease by 20%.

100% = the amount−20%80%
100%−20%=80%
80÷100=0.8multiplier

Find the multiplier to decrease by 5%.

100% = the amount−5%95%
100%−5%=95%
95÷100=0.95multiplier

Copy and complete the table.

Decrease by10%40%25%70%12%2%
New percentage90%60%75%30%88%98%
Multiplier0.90.60.750.30.880.98

Why does × 0.8 decrease by 20%?

100% = £50−20%80% = £40100% of £5050 × 1 = 5020% of £5050 × 0.2 = 1080% of £5050 × 0.8 = 40

Decrease £70 by 20%.

100% = £70−20%80% = £56
100%−20%=80%
80÷100=0.8multiplier
70×0.8multiplier=56

Decrease £80 by 15%.

100% = £80−15%85% = £68
100%−15%=85%
85÷100=0.85multiplier
80×0.85multiplier=68

Decrease £70 by 20%.

100% = £70−20%80% = £56
100%−20%=80%
80÷100=0.8multiplier
70×0.8multiplier=56

Decrease £45 by 40%.

100% = £45−40%60% = £27
100%−40%=60%
60÷100=0.6multiplier
45×0.6multiplier=27

Decrease £70 by 20%.

100% = £70−20%80% = £56
100%−20%=80%
80÷100=0.8multiplier
70×0.8multiplier=56

Decrease £300 by 5%.

100% = £300−5%95% = £285
100%−5%=95%
95÷100=0.95multiplier
300×0.95multiplier=285

Decrease £70 by 20%.

100% = £70−20%80% = £56
100%−20%=80%
80÷100=0.8multiplier
70×0.8multiplier=56

A candle is 20 cm tall. Its height goes down by 25%. How tall is it now?

100% = 20 cm−25%75% = 15 cm
100%−25%=75%
75÷100=0.75multiplier
20×0.75multiplier=15

Decrease £60 by 30%. Which calculation is right?

A60 × 0.3
B60 × 0.7
C60 × 1.3
D60 − 30
A: found only the 30% (£18): take it away from 100% firstB: rightC: added to 100%: that is an increase (£78)D: took away £30, not 30%

Percentage decrease with a multiplier worksheet, page 1

Percentage decrease with a multiplier worksheet, page 2

Answer sheet

Is it right?
Thumbs up: right. Thumbs down: wrong.

  1. Decrease 40 by 30%. 40 × 0.7 = 28

    Right

  2. Decrease 20 by 5%. 20 × 0.5 = 10

    Wrong: 5% off leaves 95%, so 0.95. The answer is 19.

  3. Decrease 90 by 20%. 90 × 0.2 = 18

    Wrong: that is only the 20%. Use 0.8.

  4. Decrease 90 by 10%. 90 × 0.9 = 81

    Right

  5. Decrease 70 by 10%. 70 − 10 = 60

    Wrong: take away 10%, not 10. The answer is 63.

  1. Decrease £45 by 20%.

    £36

  2. A phone costs £250. The price goes down by 8%. What is the new price?

    £230

  3. What is the multiplier to decrease by 50%? What happens to the amount?

    0.5. It halves.

  4. Jo decreases £80 by 10%. Then she decreases the answer by 10%. Is that the same as decreasing £80 by 20%?

    No. £64.80, not £64

  5. A price goes up by 20%. What is the multiplier?

    1.2 (100% + 20% = 120%)

  1. Decrease £90 by 30%.

    £63
    100% = £90−30%1Take awayfrom 100%.100%30%70%−=2Divideby 100.100÷=3Multiply.×=

  2. Decrease £40 by 15%.

    £34
    100% = £40−15%1Take awayfrom 100%.100%−=2Divideby 100.100÷=3Multiply.×=

  3. Decrease £200 by 4%.

    £192
Exit tickets to print