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1. 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?

A. Rs. 7.98

B. Rs. 8

C. Rs. 8.50

D. Rs. 9

Solution:

Total quantity of petrol consumed in 3 years

\begin{aligned} = (\frac{4000}{7.50} + \frac{4000}{8} + \frac{4000}{8.50}) litres \\ = 4000 (\frac{2}{15} + \frac{1}{8} + \frac{2}{17}) litres \\ = \frac{76700}{51} litres \\ Total amount spent \\ = R s . (3 \times 4000) \\ = R s . 12000 \\ ∴ Average Cost \\ = R s . \frac{12000 \times 51}{76700} \\ = R s . \frac{6120}{767} \\ = R s . 7.98 \end{aligned}

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