A class of urn problems is associated with coupon collection. There are n different coupons(an indefinite supply of balls of n different colors in an urn from which we sample without replacement) that come with a product. The coupons are obtained at random,each purchase generates a coupon numbered from 1 to n.When a coupon is collected the buyer keeps it,and the company replaces the product in the market.How soon does the collector get all n different coupons?