The local CD shop operates an unusual discount policy. The discount on the next purchase is worked out on the current purchase in the following way: for every whole pound spent you get 0.5% discount on the next purchase. For example, if you purchased £8.99 on the first purchase, you would then get a 4% discount on the next purchase and so on. You can make as many purchases as necessary.
You need to buy 7 CDs, costing, £11.50, £12.00, £12.00, £12.50, £13.00, £13.00 and £14.50 - what is the cheapest method of buying them?