How many liters of pure water should be mixed with a 7 liter solution of 60% acid to produce a mixture that is 90% water?

Question

How many liters of pure water should be mixed with a 7liter solution of 60% acid to produce a mixture that is 90% water?

Answer 1

If the mixture is 90% water, one can assume it is 10% acid.  Thus...

(7 L)(60% acid) = (x L)(10% acid)

x = 42 liters final volume

Liter of 100% water to be added = 42 L - 7 L = 35 liters