Question 40

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waecmaths 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

Option A: 

$22\tfrac{1}{2}km$ 

Option B: 

30km

Option C: 

$33\tfrac{3}{4}km$

Option D: 

$45km$

waecmaths solution: 

$\begin{align}  & R\propto {{d}^{2}} \\ & R=k{{d}^{2}} \\ & 4=k{{(15)}^{2}} \\ & k=\frac{4}{225} \\ & \text{When }R=9 \\ & 9=\frac{4}{225}{{d}^{2}} \\ & {{d}^{2}}=\frac{9\times 225}{4} \\ & d=\sqrt{\frac{9\times 225}{4}}=\frac{3\times 15}{2}=22.5 \\\end{align}$

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