1. WORKING BACKWARDS Example1 - Appreciation 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 (a)

2. NB: We do not take away 20% !!!! Suppose her speed increased by 20% and she is now travelling at 72km/hr. What was her speed before reaching the steep part? (b) ************** 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 leaves65% 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. New level = 0.65 X old level then So 78 litres = 0.65 X old level So old level = 78 litres  0.65 = 120 litres