Permutations and Combinations
Message posted by Hung Cheung (via 193.132.229.110) on March 21, 2001 at 10:50 AM (ET)

I want to test launch a magazine that includes collectible cards (eg football stickers etc etc) as a giveaway each week.

There are 320 cards in the set.

There will be eight different cards in each of the 50 issues - ie collect all 50 issues and you will end up with 400 cards, including a certain amount of duplicates.

The sets of eight cards will not be circulated as the same batch of eight each week.

Is eight cards per issue enough to ensure that a reader who collects all 50 issues will have a 75% chance of collecting all 320 different cards? If not, how many per issue is enough?

I'm sure this is a simple one from school but can't remember how to work out the answer - can you help?

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Re: Permutations and Combinations
Message posted by Phil (via 165.247.230.11) on March 23, 2001 at 12:49 AM (ET)

That already puts you below the 75% chance and we haven't even calculated the probability of 2 cards missing yet.

With your scheme, very few people will get a 100% complete set.

Maybe someone else can tell you how many to give out to hit your 75% goal. I suggest you send out most of the cards on a scheduled basis and then only make some of the cards randomized (e.g. everyone gets the same six and one or two a week are random).