A tank is full of pure petrol. Each time, 20% of the contents are drained and replaced with kerosene. After three such operations, what percentage of the tank is petrol?
Correct answer D. 51.2%
Explanation
Petrol fraction = (1 - 0.2)^3 = 0.512, so petrol makes up 51.2%. Subtracting 20% three times (40%) ignores that later draws contain kerosene.
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