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The rate of consumption of petrol by a vehicle ... - WAEC Mathematics 2015 Question

The rate of consumption of petrol by a vehicle varies directly as the square of the distance covered. If 4 litres of petrol is consumed on a distance of 15km. how far would the vehicle go on 9 litres of petrol?
A
22\(\frac{1}{2}\)km
B
30km
C
33\(\frac{1}{2}\)km
D
45km
correct option: a

R (\alpha) D2

R = D2K

R = 4 Litres when D = 15cm

thus; 4 = 152k

4 = 225k

k = (\frac{4}{225})

This gives R = (\frac{4D^2}{225})

Where R = 9litres

equation gives

9 = (\frac{4D^2}{225})

9 x 225 = 4d2

D2 = (\frac{9 \times 225}{4})

D = (\sqrt{9 \times 225}{4})

= (\frac{3 \times 15}{2})

= 22(\frac{1}{2})km

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