30 litres of a 20% acid solution are mixed with 20 litres of a 45% acid solution. What is the strength of the mixture?

Explanation

1. 01

   Acid in each: $0.2 \times 30 = 6$ litres and $0.45 \times 20 = 9$ litres, 15 litres in 50.

2. 02

   $\frac{15}{50} = 30\%$.