mynameisjanelle
In how many ways can a gymnastics team of 4 be chosen from 9 gymnasts?



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mynameisjanelle
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dont get this one, could someone show me the steps?

lgbasallote
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"chosen" so you use combinations

apple_pi
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from 9 choose 4.
9C4 = ...

lgbasallote
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arent you missing something?

mynameisjanelle
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362880?

lgbasallote
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that's 9!

apple_pi
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don't forget to divide by all the same combinations (nr)!

lgbasallote
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\[9C4 \implies \frac{9!}{4!(94)!}\]

apple_pi
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dividing by (nr)! is what separates the combination formula from the permutation, because you are not counting all the different arrangements

lgbasallote
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isnt dividing r! what separates it?

lgbasallote
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\[nCr = \frac{n!}{r!(nr)!}\]
\[nPr = \frac{n!}{(nr)!}\]

lgbasallote
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dividing by r! is just the difference i see =))

mynameisjanelle
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126!!

lgbasallote
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i hope those ! arent factorials :p haha

lgbasallote
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anyway yeah. 9C4 = 126

mynameisjanelle
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ya:P

apple_pi
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Ooops, I meant r! not (nr)! for all the above posts. Sorry :o