A cask holds 80 litres of juice. 8 litres are drawn off and replaced with water, and then 8 litres of the mixture are drawn off and replaced with water again. What is now the ratio of juice to water?

Explanation

1. 01

   Juice left $= 80 \times \left(\frac{72}{80}\right)^{2} = 80 \times 0.81 = 64.8$ litres; water $= 80 - 64.8 = 15.2$ litres.

2. 02

   $64.8 : 15.2 = 81 : 19$.