A lady goes to the well with two jugs. One holds exactly three quarts and the other holds exactly five quarts. She needs exactly four quarts of water for her soup. Using inly two jugs, which she cannot mark in any way, how can she get four quarts?

The question is answered using logic.

We have two jugs that have capacity of three quarts and five quarts respectively.

Since we want water of four quarts, definitely it will be in the five quarts jug since the three quarts jug cannot contain four quarts of water.

Let represent the five quarts jug and three quarts jug as x and y. (x, y)

First Step: the both jug are empty = (0, 0)

Second Step: the five quarts jug is filled, while the three quarts jug is still empty = (5, 0)

Third Step: the five quarts jug is poured into the three quarts jug, remain just two quarts in the five quarts jug = (5-3, 0+3) = (2, 3)

Fourth Step: the three quarts jug is emptied to the ground = (2, 3-3) = (2, 0)

Fifth Step: the remaining water of the five quarts jug is emptied to the three quarts jug = (0, 2)

Sixth step: the five quarts jug is filled again = (5, 2)

Seventh step: the water from the five quarts jug is used to fill the three quarts jug which has space for just one quarts = (5-1, 2+1) = (4, 3)

Finally, we can have a four quarts water in the five quarts jug with the three quarts jug also filled or the content of the three quarts can be poured away and we have the five quarts having four quarts while the three quarts is empty.