Question 30192
Let x = amount of pure acid added.


So how much of the 10% acid was there? Easy... everything else to make up the 54litres...so (54-x).


Now we say BEFORE = AFTER


BEFORE is (1.00*x) + (0.10*(54-x))
AFTER is 0.20*54


so (1.00*x) + (0.10*(54-x)) = 0.20*54
x + 5.4 - 0.1x = 10.8
0.9x + 5.4 = 10.8
0.9x = 5.4
x = 5.4/0.9
x = 6 litres


So we need 6 litres of the pure acid and also 48 litres of the 10% acid solution.


jon.