Question

How much pure alcohol must be added to 400 ml of a 15% solution to make its strength 32%

Answer 1

Quantity of alcohol =400*15/100 = 60ml
x is pure alcohol which must be added : (x + 60)/(x + 400) = 32/100
100x + 6000 = 32x + 12800 => 68x = 6800 => x = 100
100ml pure alcohol must be added