Question 576224
A chemist has 10 quarts of 10% of acid. She wishes to add enough water to reduce it to a 4% solution. How many quarts of water must she add?
sol:
 10 q has 10% of acid this implies 1 q is acid , 9q is water
acid and water are in the ratio 1 : 9
in the new solution only 4% is acid ,remaining is water they are in the ratio    1 :24 
let x be the volume of water added .
1/( 9x) = 1/24
solving for x you get 15 quarts.