Question 1122201
Check your answer.  If a cistern holds 450 gallons, 3/4 full it holds 337.5 gallons.  When 40 gallons of that are removed, it holds 297.5 gallons, not quite 2/3.

Full cistern=x
it is (3/4)x
(3/4)x-40=(2/3)x
(1/12)x=40
x=480 gallons
3/4 full is 360 gallons, and 40 removed leaves 320 gallons, which is 2/3.
Yes, it is what you wrote about.