SusieQ Posted September 19, 2013 Share Posted September 19, 2013 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. Quote Link to comment Share on other sites More sharing options...
Macaroon Posted August 31, 2014 Share Posted August 31, 2014 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 Quote Link to comment Share on other sites More sharing options...
Playscape Posted September 1, 2014 Share Posted September 1, 2014 That is a lot of combinations. Also, in the formula, what do the exclamation marks mean? Quote Link to comment Share on other sites More sharing options...
Macaroon Posted September 1, 2014 Share Posted September 1, 2014 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.) Quote Link to comment Share on other sites More sharing options...
Playscape Posted September 1, 2014 Share Posted September 1, 2014 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. Quote Link to comment Share on other sites More sharing options...
trtpmtxp Posted February 18, 2015 Share Posted February 18, 2015 thanks i also have the same problem... Quote Link to comment Share on other sites More sharing options...
gracegrace Posted December 5, 2016 Share Posted December 5, 2016 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! :distracted: Quote Link to comment Share on other sites More sharing options...
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