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Thread: I have a math question

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    Trying to make mom and pop proud
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    Question I have a math question

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    Using the numbers 1 through 44, how many sets of 4 different numbers are possible? No number can be repeated and the number 0 cannot be used. Is there a formula for figuring this out?
    I can find the number of all possible numbers with no repetitions, but I can figure out how many SETS of 4 numbers are possible.
    All help is greatly appreciated.

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    Trying to make mom and pop proud Macaroon's Avatar
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    The formula is (n!/(n-r)!), where n is the things that you have and r is the amount of things you want in your set. This is assuming order matters, because (40, 19, 27, 5) is different from (5, 27, 40, 19).

    So, based on that formula, you get:

    44 * 43 * 42 * 41 = 3,258,024

    If you have further issues with these types of problems, try this link: Combinations and Permutations

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    Muzzled. Playscape's Avatar
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    That is a lot of combinations. Also, in the formula, what do the exclamation marks mean?

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    Trying to make mom and pop proud Macaroon's Avatar
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    The exclamation marks are a symbol used for taking a factorial, which multiplies all whole numbers up to and including the number you're doing the operation on.

    So, 5! = 5*4*3*2*1 = 120.

    Since the formula is a fraction, where I happened to get that from is this:

    44! / (44-4)!

    We can expand 44! a little bit to make our lives easier.

    44 * 43 * 42 * 41 * 40! / 40!

    The 40! on both parts of the fraction cancel, leaving you with that leftover multiplication to do.

    Mind you, this is a permutation- order does matter. If we received from the prompt that order was irrelevant, we would approach this differently. (Combinations actually have less choices than permutations because of this; (9,0) is the same thing as (0,9) in combination-land. Permutations would have these be two different possibilities added to the count.)

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    Muzzled. Playscape's Avatar
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    Cool, thanks. I have one more question: I like to listen to lectures and such on my MP3 player, so does anyone know where I could download some free lectures or audiobooks relating to algebra and geometry? I need to brush up on those skills before I go back to school. Thanks.

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    Re: I have a math question

    thanks i also have the same problem...

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    Thumbs up Re: I have a math question

    Quote Originally Posted by Playscape View Post
    Cool, thanks. I have one more question: I like to listen to lectures and such on my MP3 player, so does anyone know where I could download some free lectures or audiobooks relating to algebra and geometry? I need to brush up on those skills before I go back to school. Thanks.
    You can find some audiobooks here - Mathematics Audio Books, Podcasts, and Videos - but I don't know if the books are any good. If you will download some of them, please, tell what you think about them. And another good resource here.

    Hope this might help!

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