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4.Average
hard
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
