You have a hose along with a 3 liter bucket and a 5 liter bucket. How do you get exactly 4 liters of water?

First, fill the 3 liter bucket and pour it into the 5 liter one. Then, re-fill the 3 liter bucket and pour it into the 5 liter bucket until it’s full – that leaves 1 liter in the 3 liter bucket and 5 in the 5 liter bucket.

Then, pour out the 5 liter bucket so nothing is left and pour the 1 liter of water from the 3 liter bucket into the 5 liter bucket. Finally, fill the 3 liter bucket completely and pour it into the 5 liter bucket – since it already has 1 liter of water, you’ll get exactly 4 liters.

For this type of question, it’s easiest to use deductive reasoning to get the answer. You know you can’t possibly get 4 liters of water in the 3 liter bucket – it has to be in the 5 liter bucket.

Since you can easily get 3 liters of water, that tells you that the “trick” will involve isolating the remaining 1 liter and getting it into the 5 liter bucket. So then the question comes down to how to get the 1 liter of water in the 3 liter bucket. You know it has to involve pouring water into the 5 liter bucket, and that leads you in the right direction.