You have 3 containers, labelled A, B and C.
Container A has a capacity of 8 litres; container B has a capacity of 5 litres; container C has a capacity of 3 litres.
Currently, container A is full to the brim with water, whereas B and C are empty.
You are allowed to transfer water from any one container to the other, but are not allowed to use external water sources such as taps (so no pouring water down the drain and re-filling). You have no access to measuring equipment, and you are not allowed to 'guesstimate' water levels by eye (so, for instance, you cannot pour water from A to B and then do a visual check that they are approximately the same level, or 'half full').
What steps do you need to take to get to a state where 4 litres of water are in A, 4 litres of water are in B, and C is empty?