Percentage Decrease Calculator Demonstration This resource provides animated
- Slides: 19
Percentage – Decrease – Calculator – Demonstration This resource provides animated demonstrations of the mathematical method. Check animations and delete slides not needed for your class.
÷ 2 How can we quickly find these percentages of 130? ÷ 4 ÷ 5 170 ÷ 10 50% 85 25% 42. 5 20% 34 10% 17 5% 1% 8. 5 1. 7 ÷ 2 ÷ 10
How many different methods can you think of? Find 35% of 300.
Odd one(s) out? Which words don’t belong in this list? Decrease Decline Less Fractionise Reduction Shrink Loss Discount Depreciate Contract
These shoes are normally £ 80 In the sale they are 35% off! How much do the shoes cost now? 5% 10% 10% 4 8 8 £ 80 100% 65% 80 − 8 − 8 − 4 = 80 − 28 = £ 52 We can find 35% & subtract that from the original amount. 8
DEMO Decreasing by a Percentage Decrease 50 by 10% Find 10% = 5 Original − 10% 50 − 5 = 45
DEMO Decreasing by a Percentage Decrease 80 by 30% Find 30% × 3 10% = 8 30% = 24 Original − 30% 80 − 24 = 56
DEMO YOUR TURN Decreasing by a Percentage Decrease 80 by 30% Find 30% × 3 Decrease 70 by 40% Find 40% 10% = 8 30% = 24 Original − 30% 80 − 24 = 56 × 4 10% = 7 40% = 28 Original − 40% 70 − 28 = 42
DEMO Decreasing by a Percentage Decrease 220 by 15% Find 15% + 10% = 22 5% = 11 15% = 33 Original − 15% 220 − 33 = 187
DEMO Decreasing by a Percentage Decrease 40 by 45% Find 45% × 4 10% = 4 40% = 16 5% = 2 45% = 18 Original − 45% 40 − 18 = 22
DEMO YOUR TURN Decreasing by a Percentage Decrease 40 by 45% Find 45% × 4 10% = 4 40% = 16 5% = 2 45% = 18 Original − 45% 40 − 18 = 22 Decrease 160 by 35% Find 35% × 3 10% = 16 30% = 48 5% = 8 35% = 56 Original − 35% 160 − 56 = 104
DEMO Decreasing by a Percentage Decrease 40 by 45% Find 45% × 4 10% = 4 40% = 16 5% = 2 45% = 18 a) Decrease 120 by 10% YOUR TURN 108 b) Decrease 80 by 15% 68 c) Decrease 160 by 45% 88 d) Decrease 400 by 21% 316 e) Decrease 700 by 6% 658 f) Decrease 90 by 43% 51. 3 g) Decrease 60 by 2. 5% 58. 5 Original − 45% 40 − 18 = 22
Using decimals to find a percentage of a quantity. 300% = 80 × 3 80 80 200% = 80 × 2 80 100% = 80 × 1 80 50% = 80 × 0. 5 40 80 80
Using decimals to find a percentage of a quantity. 100% = 90 × 1 90 50% = 90 × 0. 5 45 75% = 90 × 0. 75 67. 5 27% = 90 × 0. 27 24. 3
Use a decimal to calculate these percentages of quantities. 100% = 70 × 1 100% = 270 × 1 70 270 50% = 70 × 0. 5 75% = 270 × 0. 75 45 202. 5 20% = 70 × 0. 2 32% = 270 × 0. 32 14 86. 4 90% = 70 × 0. 9 63 35% of 70 = 24. 5 67% = 270 × 0. 67 180. 9 12. 5% of 270 = 33. 75
Decreasing using a Decimal Multiplier 0. 7 1 Decrease 90 by 30% 100% 30% 0. 3 90 × (1 − 0. 3) = 90 × 0. 7 = 63
Decreasing using a Decimal Multiplier 0. 85 1 Decrease 140 by 15% 100% 15% 0. 15 140 × (1 − 0. 15) = 140 × 0. 85 = 119
Decreasing using a Decimal Multiplier 0. 85 1 Decrease 140 by 15% 100% 15% 0. 15 140 × (1 − 0. 15) = 140 × 0. 85 = 119 a) Decrease 160 by 20% 128 e) Decrease 510 by 34% 336. 6 b) Decrease 280 by 70% 84 f) Decrease 230 by 81% 43. 7 c) Decrease 150 by 25% 112. 5 g) Decrease 270 by 5% 256. 5 d) Decrease 310 by 35% 201. 5 h) Decrease 350 by 3. 5% 337. 75
Questions? Comments? Suggestions? …or have you found a mistake!? Any feedback would be appreciated . Please feel free to email: tom@goteachmaths. co. uk
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