WORKING BACKWARDS

1
WORKING BACKWARDS
Example1 - Appreciation
A downhill skier increases her speed by 20 when
she reaches a steep section.
(a)
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
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(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