posted by Jeff .
If you had one gallon of concentrated hydrochloric acid (12 N) and added water to make dilute hydrochloric acid (6 N), how much dilute hydrochloric acid would you have?
You would have two gallons of solution.
vol x N = vol x N
1 gallon x 12N = gallons x 6N
vol =12/6 = 2 gallons.