There are always some strange little problems in life, like this "how to use 3L and 5L empty cups to get 4L of water from the faucet", which looks simple, but actually has to use a little brain.

Let's talk about these two cups first, one with a 3-liter capacity and the other with a 5-liter capacity, and the faucet can receive unlimited water.

So how do you get 4 liters? In fact, the steps are not difficult, let's take them step by step. First, fill the 5L cup with water, at this time the 5L cup is full and the 3L cup is empty. Then, use the water in the 5L cup to fill the 3L cup, because the 3L cup is empty, after pouring, there will be 5-3=2L of water left in the 5L cup, and the 3L cup will be full. At this time, pour out all the water in the 3L cup, let it turn back into an empty cup, and then pour the remaining 2L water in the 5L cup into the 3L cup.

Then, fill the 5L cup with water, and then use the water in the 5L cup to pour the 3L cup, because there is already 2L of water in the 3L cup, and you can fill it with another 1L, so after pouring, the remaining water in the 5L cup is 5-1=4L, which will get the 4L water you want.

In fact, many things in life are like this, it seems that you have to rely on "precise calculations", the actual disassembly steps, and slowly turn it upside down.

Just like dividing snacks, you have to divide them fairly among your friends, or organize things and classify them according to steps, which is similar to the reason. When encountering this kind of small challenge, don't panic, step by step, you can find a way, it's quite interesting, just like playing a puzzle-solving game, there is a sense of accomplishment to solve it, you can also try it, feel the fun of "pouring water to solve the problem".