Question

Acar owner buyspetrol at Rs 7.50, Rs 8.00 and Rs 8.50 per litre for three successive years. What approximately is the average costper litre of petrol if he spends Rs 4000 each year?

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

Answer 1

Answer: (C)

Rs 7.98

Answer 2

Given in the question that the amount spend each year is constant, thus average cost is the harmonic mean of each price.

$3 ÷ (\frac{1}{7.5} + \frac{1}{8} + \frac{1}{8.6})$

= $3 ÷ (\frac{2}{15} + \frac{1}{8} + \frac{2}{17})$

$$= $3 ÷ (\frac{272 + 255 + 240}{2040})$

= $3 \times \frac{2040}{767}$ = 7.98

The correct option is (C):7.98