Despite having stressed the importance of knowing the costs involved in making a product or providing a service, they are not always easy to identify. Imagine that you buy a box of 10 computer disks for £15 on Friday. On Sunday a friend asks you to sell him one for some urgent work he is doing. You know that if you were to replace that single disk on Monday it would cost you £2.00. What is the cost of the disk?

(a) £1.50

(b) £2.00

(c) Both these figures

(d) Neither of these figures