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Cpp - 3 and a 5 litre water container puzzles

You have a 3 and a 5 litre water container, each container has no markings except for that
which gives you it's total volume. You also have a running tap. You must use the containers and the
tap in such away as to exactly measure out 4 litres of water. How is this done?

Ans:

Number 1

Fill the 5 litre can from the tap
Empty the 5 litre can into the 3 litre can - leaving 2 litres in the 5 litre can.
Pore away the contents of the 3 litre can.
Fill the 3 litre can with the 2 litres from the 5 litre can - leaving 2 litres in the 3 litre can.
Fill the 5 litre can from the tap.
Fill the remaining 1 litre space in the 3 litre can from the 5 litre can.
Leaving 4 litres in the 5 litre can.

Number 2

Fill the 3 litre can from the tap.
Empty the contents of the 3 litre can into the 5 litre can.
Fill the 3 litre can from the tap.
Empty the contents of the 3 litre can into the 5 litre can. - Leaving the 5 litre can full and 1 litre in the 3 litre can.
Pore away the contents of the 5 litre can
Pore the 1 litre from the 3 litre can into the 5 litre can.
Fill the 3 litre can from the tap.
Empty the contents of the 3 litre can into the 5 litre can.
Leaving 4 litres in the 5 litre can.