Hello, nertil1!
Another classic problem . . .
You have a cup of tea and a barrel of whiskey.
You take one teaspoon of tea from the cup and you put it in the whiskey.
You then take one teaspoon of the mixture and put it in the tea cup.
Is there more whiskey in the tea cup or is there more tea in the whiskey barrel? Code:
* *
|---------------|
|///////////////|
|///////////////|
|///////////////|
* * |///////////////|
|-----------| |/// Whiskey ///|
|:::::::::::| |///////////////|
|:::::::::::| |///////////////|
|::: Tea :::| |///////////////|
|:::::::::::| |///////////////|
*-----------* *---------------*
Since one teaspoon of liquid is removed from the cup
. . and then one teaspoon of liquid is replaced in the cup,
both containers have their original amounts of liquid.
Some amount of whiskey is now in the teacup;
. . we don't know exactly how much.
But we do know that that amount of whiskey
. . displaces an equal amount of tea, which is now in the barrel. Code:
* *
|---------------|
|::::: Tea :::::|
|---------------|
|///////////////|
* * |///////////////|
|-----------| |/// Whiskey ///|
|/ Whiskey /| |///////////////|
|-----------| |///////////////|
|::: Tea :::| |///////////////|
|:::::::::::| |///////////////|
*-----------* *---------------*
QED . . . The amounts are equal.