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?

When equal money is spent, the appropriate average is the harmonic mean. HM = n/(Σ(1/xᵢ)) = 4/(1/150 + 1/200 + 1/250 + 1/300). LCM-based: 1/150 + 1/200 + 1/250 + 1/300. Computing: 1/150 ≈ 0.00667, 1/200 = 0.005, 1/250 = 0.004, 1/300 ≈ 0.00333. Sum ≈ 0.019. HM ≈ 4/0.019 ≈ 210.5. So approximately 210.