A car owner buys petrol at Rs.,7.50, Rs., 8 and Rs., 8.50 per litre for three successive years. What

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A car owner buys petrol at $Rs.\,7.50, Rs.\, 8$ and $Rs.\, 8.50$ per $litre$ for three successive years. What approximately is the average cost per litre of petrol if he spends $Rs.\, 4000$ each year ?(in $Rs.$ )

A

$7.98$

B

$8$

C

$8.50$

D

$9$

Solution

In the first year petrol consumed $=\frac{4000}{7.5}$ litres

In the second year petrol consumed $=\frac{4000}{8}$ litres

In the third year petrol consumed $=\frac{4000}{8.5}$ litres

Average price/litre of petrol $=\frac{4000 \times 3}{\frac{4000}{7.5}+\frac{4000}{8}+\frac{4000}{8.5}}$

$=\frac{3 \times 7.5 \times 8 \times 8.5}{8 \times 8.5+7.5 \times 8.5+7.5 \times 8}$

$=\frac{1530}{68+63.75+60}=\frac{1530}{191.75}$

$=$ $Rs. \,8 /litre$

Standard 13

Quantitative Aptitude

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