riddle of the day

A problem with an unusual quality: the desired quantity does not exist in any jar, it must be built. Every transfer matters, and the order is not arbitrary.

The water jugs

Curious
Pure logic

Riddle statement

You have two unmarked jugs: one with 3 liters and one with 5 liters. You have a tap with unlimited water.

How can you measure exactly 4 liters?

Show solution

Solution

Answer: Yes: you can leave exactly 4 liters in the 5 liter jug.

Explanation:

  1. Fill the 5 liter jug.
  2. Pour it into the 3 liter container until it is full. There are 2 liters left in the 5.
  3. Empty the 3 liter jug.
  4. Transfer those 2 liters to the 3-liter jug.
  5. Fill the 5 liter jug again.
  6. Pour from the 5 to the 3 only until the latter is complete.

As the 3 jug already had 2 liters, it only accepts 1 more liter. That liter comes out of the 5-size jug, so there are exactly 4 liters left in it.