A tank holds 64 litres of pure oil. Each time, 16 litres are removed and replaced with kerosene. After how many such operations will the tank contain 27 litres of oil?
Correct answer C. 3
Explanation
Each operation leaves 3/4 of the oil. Oil left = 64 x (3/4)^n = 27, so (3/4)^n = 27/64 = (3/4)^3, giving n = 3.
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