A can holds 40 litres of pure juice. Some juice is drawn out and replaced with water, and the operation is repeated with the same amount. The can now has 25.6 litres of juice. How many litres were drawn out each time?

Explanation

1. 01

   $40 \times \left(1 - \frac{x}{40}\right)^2 = 25.6$, so $\left(1 - \frac{x}{40}\right)^2 = 0.64$.

2. 02

   $1 - \frac{x}{40} = 0.8$, so $\frac{x}{40} = 0.2$.

3. 03

   $x = 0.2 \times 40 = 8$ litres.