The owner of a canteen proposed the following test to a man who wanted to be hired as a waiter:
Here you have a barrel, fill it with water exactly halfway, neither more nor less, without using any stick, rope or any other object to measure.
How did the waiter pass the test?
If the barrel is filled with water exactly halfway, then, tilting it to such an extent that the water level reaches just the edge of the barrel, we will see that the water level reaches exactly the top point of the bottom of the barrel as shown. in the illustration to) image and we will have the full barrel exactly halfway.
This happens by the fact that we draw a plane that passes through two diametrically opposite points of the upper and lower circles of the barrel, this plane divides the barrel into two equal parts, one empty and the other full.