A drum holds 80 litres of pure coconut oil. 8 litres are removed and replaced with a cheaper oil, and this is done three times in all. How much coconut oil is left in the drum?

Explanation

1. 01

   Each operation keeps $\frac{80 - 8}{80} = 0.9$ of the coconut oil.

2. 02

   After three operations: $80 \times 0.9^3 = 80 \times 0.729 = 58.32$ litres.