I should like to say straightaway that collecting cigarette-cards is not my hobby But recently the manufacturers of the brand of cigarette I smoke started to issue an attractive series of cards and I said to a friend, “I think I shall save these cards until I obtain the complete set of fifty.” He replied, “About how many packets do you think you will have to buy before you get the set?” And this raises an interesting problem in probability which I do not recollect having seen before.