Decrease by a percentage | Exit Quiz | Oak National Academy

Decrease 40 by 20%.

Answer explanation

100% − 20% = 80%, so decreasing by 20% is the same as finding 80%. 0.8 × 40 = 32 or 10% = 4, 20% = 8 so a decrease of 20% is 40 − 8 = 32.

Decrease 700 by 30%.

Answer explanation

100% − 30% = 70%, so decreasing by 30% is the same as finding 70%. 0.7 × 700 = 490 or 10% = 70, 30% = 210 so a decrease of 30% is 700 − 210 = 490

Match each question to an equivalent question.

• Decrease 450 by 20%

• Work out 88% of 450

• Decrease 450 by 80%

• Work out 80% of 450

• Decrease 450 by 1.2%

• Work out 98.8% of 450

• Decrease 450 by 12%

• Work out 20% of 450

Answer explanation

When increasing (or decreasing) an amount by a percentage, it is important to know the equivalent question can be phrased in different ways. 100% − 12% = 88%, so decreasing by 12% is the same as finding 88%.

Match each statement with the correct multiplier.

• Decrease by 22%

• ×0.98

• Decrease by 80%

• ×0.92

• Decrease by 2%

• ×0.2

• Decrease by 8%

• ×0.78

Answer explanation

100% − 22% = 78%, so decreasing by 22% is the same as finding 78%. Finding 78% of an amount is the same as multiplying by 0.78

Decrease 600 by 39%.

Answer explanation

100% − 39% = 61%, so the multiplier is 0.61. Using an area model or the column method to work out the 0.61 × 600 = 366

Match each calculation to its answer.

• Decrease 800 by 52%

• 384

• Decrease 70 by 2%

• 363.4

• Decrease 460 by 21%

• 68.6

• Decrease 400 by 12%

• 352

Answer explanation

Decrease 460 by 21% = 0.79 × 460. Decrease 800 by 52% = 0.48 × 800. Decrease 70 by 2% = 0.98 × 70. Decrease 400 by 12% = 0.88 × 400.