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Math Help - Number of ways

  1. #1
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    Number of ways

    Suppose you own 30 cassette tapes and 20 cds. If you wish to selct 5 taps and 3 cds to take on a trip with you, in how many ways can you make you selections?

    Can anyone explain how to do this for me?
    thanks
    Last edited by mr fantastic; September 30th 2009 at 11:16 PM.
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  2. #2
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    Recall ^{n}C_r = \frac{n!}{r!(n-r)!}

    Cassettes: Choose 5 from 30 ^{30}C_5

    CDs: Choose 3 from 20 ^{20}C_3

    Total: ^{30}C_5+^{20}C_3
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  3. #3
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    Quote Originally Posted by pickslides View Post
    Recall ^{n}C_r = \frac{n!}{r!(n-r)!}

    Cassettes: Choose 5 from 30 ^{30}C_5

    CDs: Choose 3 from 20 ^{20}C_3

    Total: ^{30}C_5+^{20}C_3
    so what exactly does the ^{30}C_5+^{20}C_3 mean
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  4. #4
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    ^{30}C_5 = \frac{30!}{5!(30-5)!}

     ^{20}C_3 = \frac{20!}{3!(20-3)!}

    does this help?
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