A chemist pours 12 litres of a solution with acid and water in the ratio $2 : 3$ into 8 litres of a solution with acid and water in the ratio $4 : 1$. What percentage of the combined solution is acid?

Explanation

1. 01

   Acid from the first = $\frac{2}{5} \times 12 = 4.8$ litres.

2. 02

   Acid from the second = $\frac{4}{5} \times 8 = 6.4$ litres.

3. 03

   Acid % = $\frac{4.8 + 6.4}{20} \times 100 = \frac{11.2}{20} \times 100 = 56\%$.