I want to buy 1 litre of milk. My options are to either buy 250ml bottles for £1 each or 500ml bottles for £1.50 each. Which is the cheapest way for me to buy 1 litre of milk?

If you were to buy 250ml bottles you would need four meaning - 250 x 4 = £1 x 4 = £4.

If you were to buy 500ml bottles you would need two meaning - 500 x 2 = £1.50 x 2 = £3.

Therefore it is cheaper to buy two 500ml bottles of milk.