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dreamspace
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Homework Statement
Suppose that I'm collecting cards, and that in a complete collection there are m items.
When buying a new card, there's an equal probability that the card is any of those m cards.
Let X be the number of cards I need to buy in order to get a complete collection
What is the Expectation/Ex of X? What is the Standard Deviation?
Homework Equations
Let [itex]X = \sum^{m}_{i=1} X_{i} [/itex], where [itex] X_{i} [/itex] is the number of cards I need to buy in order to get a new type of card when I already have i - 1 different types of cards
The Attempt at a Solution
I figure this problem would involve probability mass function, but to be honest I'm stuck as I haven't had any probability or stats in over 10 years.
Any good pointers on how to go on with this problem?