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WORKING BACKWARDS

This example demonstrates how to calculate percentage increases and decreases in various scenarios, such as a skier's speed and a diver's air supply.

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WORKING BACKWARDS

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  1. WORKING BACKWARDS Example1 - Appreciation (a) A downhill skier increases her speed by 20% when she reaches a steep section. She was travelling at 50km/hr. What is her new speed? ***************** 20% increase gives 120% or 1.20. New speed = 1.20 X old speed = 1.20 X 50km/hr = 60km/hr

  2. (b) Suppose her speed increased by 20% and she is now travelling at 72km/hr. What was her speed before reaching the steep part? NB: We do not take away 20% !!!! ************** New speed = 1.20 X old speed 72km/hr = 1.20 X old speed So old speed = 72km/hr  1.20 = 60km/hr

  3. Example2 - Depreciation (a) A scuba diver uses 35% of his air during a dive. He had 80 litres. How much does he now have? ************************* 35% less leaves 65% or 0.65 New level = 0.65 X old level = 0.65 X 80 litres = 52 litres

  4. (b) Suppose the diver has used 35% of his air and now has 78 litres left. then New level = 0.65 X old level So 78 litres = 0.65 X old level So old level = 78 litres  0.65 = 120 litres

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