An edible oil is sold at the rates 150, 200, 250, 300 rupees per litre in four consecutive years. Assuming that an equal amount of money is spent on oil by a family in every year during these years, what is the average price of oil in rupees (approximately) per litre ?

Explanation

Since an equal amount of money is spent each year, the average price is the harmonic mean of the individual prices. HM = \frac{4}{\frac{1}{150} + \frac{1}{200} + \frac{1}{250} + \frac{1}{300}} = \frac{4}{\frac{20+15+12+10}{3000}} = \frac{12000}{57} \approx 210.52. The closest approximate average price is 210 rupees.

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