If you have a 4 -liter bucket and a 7-liter bucket. You need 3-liters of water for an aquarium.Explain how to get 3 liters of water if neither bucket is marked.?
You could fill the 7-liter bucket and pour water into the
aquarium until it is full, but that would make too much sense. If
you really need to have three liters, fill the 7-liter bucket
(which, although unmarked, will be larger than the 4-liter bucket)
and pour it into the 4-liter bucket. When the 4-liter bucket is
full, there will be three liters remaining in the 7-liter
bucket.