Puzzle Details

Using a tap, a container of 9 litres and a container of 4 litres...

...can you measure 6 litres?

Answer: Here are the contents of the containers after each stage:

A = 9 litres, B = 4 litres

A     B
9     0          fill A
5     4          fill B from A (leaving 5 litres in A)
5     0          empty B
1     4          fill B from A (leaving 1 litre in A)
1     0          empty B
0     1          fill B from A
9     1          fill A
6     4          fill B from A (only 3 more litres fit in B)
6     0          empty B

This leaves 6 litres in container A.

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