Question

How much acid should be added to 400 ml of 15% acid solution to increase its strength to 32%

Answer 1

The amount of acid in 15% acid of 400 ml is 60 ml.

Let x ml of acid be add to this solution.
The total volume is (400 + x), of which 32% is acid
The amount of acid in this solution is x + 60

.32(400 + x) = x + 60
128 + .32x = x + 60
0.68x = 68
x = 100 ml of acid.