Firstly you would analyse the cost of the melons in the first shop per kg. So you could buy 2 melons for £2 because they're buy one get one free and each weighs 2kg so therefore you're getting 4kg of melon for £2. £2/4 gives you price per kilogram which is 50p. Simply comparing the two price per kg's would show the cheaper one which is the second shop as you're getting the same weight but for a smaller price. In most exam boards to get the final mark a concluding statment would need to be made.