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Math Help - Permutation and Combination

  1. #1
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    Permutation and Combination

    A student decided to buy books at a bookstore. He wants to buy at least 2 books. With the amount of money he has, he can only buy a max of 3 books. There are three shelves in the book store, each shelves with the following subject : physics, chemistry, and biology. How many possible are there to make a successful purchase? (repetition is allowed)
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  2. #2
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    I think PC and CP defines the same thing right? In the end you will be buying physics and chemistry books??
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  3. #3
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    Yes, I would assume so.

    The number of selections of r objects from n types with repetition is given by

    C(n+r-1,r), where C(3+3-1,3)=10 ways for selecting 3 books and C(3+2-1,2)=6 ways for selecting 2 books
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  4. #4
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    okay, that's what I thought.. so the total possible ways would be 16 right?
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