A barrel holds 60 litres of wine. 6 litres are taken out and replaced with water, and this is done twice in all. How much wine is left?

Explanation

1. 01

   Each replacement keeps $1 - \frac{6}{60} = \frac{9}{10}$ of the wine.

2. 02

   After 2 times: $60\left(\frac{9}{10}\right)^{2} = \frac{243}{5}$ litres.