A popular example of the design of an on-line algorithm to minimize the competitive ratio is the ski-buying problem. 3 Suppose you can buy skis for $100, or you can rent skis for $10 per day. You decide to take up skiing, but you don't know if you will like it. You may try skiing for any number of days and then give it up. The merit of an algorithm is the cost per day of skis, and we must try to minimize this cost.