Using a tap, a container of 9 litres and a container of 4 litres...
...can you measure 6 litres?
Puzzle Copyright © Kevin Stone
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Hint
Fill the 9-litre container first.
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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