Question

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

A
Rs.7.98
B
Rs.8
C
Rs.8.50
D
Rs.9

Solution

## The correct option is A $$Rs. 7.98$$Total quantity of petrol consumed in $$3$$ years $$= \left (\dfrac {4000}{7.50} + \dfrac {4000}{8} + \dfrac {4000}{8.50}\right )litres$$$$= 4000\left (\dfrac {2}{15} + \dfrac {1}{8} + \dfrac {2}{17}\right )litres$$$$= \left (\dfrac {76700}{51}\right )litres$$Total amount spent $$= Rs. (3\times 4000) = Rs. 12000$$.$$\therefore$$ Average cost $$= Rs. \left (\dfrac {12000\times 51}{76700}\right ) = Rs. \dfrac {6120}{767} = Rs. 7.98$$Maths

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