How do you answer a question that asks for an object that is two-thirds full?

If something is 2/3 full, then it is 1/3 empty.

If a container contains 3 gallons of water but is only 2/3 full, then how much water can the container actually contain? To solve, just multiply the 3 gallons by 3/2 (the inverse of 2/3) to find the answer.

Why don't you try saying what the question is?

Oh dear, 2/3rds doesn't always equal 2/3rds you know.

Take a typical gastank (the kind you see outside businesses sometimes, or maybe one of those railcar tanks); if you ignore the ends (they are curved, but let's pretend they are flat) then it is easy to see that a tank 2/3rds full BY HEIGHT is not 2/3rds full BY VOLUME.

Which happens to be one of the most difficult things to calculate (more so when you take those curved end-walls into account).

The jug contains 112 litres of water.

If it is 2/3 full, how many litres does it contain?

2/3 * 112/1 = 224/3 = 74 and 2/3 litres
.....

V= L*W*H of a rectangular container