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I have a small query in selecting $r$ items out of $n$ similar items.

Is it simply $C_n^r$ or $C_n^r / r!$ ?

Thanks in advance.

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    What do you mean by n **similar** items ? Please give us an example. – 2017-01-03
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    Similar in sense for example - Tennis balls, biscuits etc... – 2017-01-03
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    You have n identical tennis balls and you select r identical tennis balls ? It doesn´t make sense to me. You should specify your question, maybe with an specific example. – 2017-01-03
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    Might want to be a little more explicit. What is C(n,r) (just explaining its definition might answer your question of whether it's the number you're looking for)? Also, 'ways' is ambiguous. Are you regarding two ways that select the same r elements in two different orders to be identical? – 2017-01-03
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    @callculus...Thanks for your comment. My question is if I were to select `r` tennis balls out of `n` tennis balls. then the number of ways of doing the same is `C(n,r)` or `C(n,r)/ r!` ?. I am having this conceptual question. – 2017-01-03
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    C(n,r) or nCr both refer the same. I don't know how to put this. Sorry for the same.. – 2017-01-03
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    @METALHEAD If the tennis balls do not distinguish then there is only one way. You just select r balls out of n balls. – 2017-01-03
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    @callculus So `nCr` we don't need here. As all are non-distinguishable we have only one way of selecting it. – 2017-01-03
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    @METALHEAD $nCr$ is the number of ways selecting n balls if you have for instance $r$ blue ball and $n-r$ yellow balls. But if the balls do not distinguish there is only one way. – 2017-01-03
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    @callculus Thank you so much for your answer... – 2017-01-03
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    @METALHEAD You are welcome. – 2017-01-03

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If given items are indentical then answer is 1.

If not identical then C(n, r).

And in case not identical you are using P(n,r). Then divided by r!.

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    Mine pleasure.. – 2017-01-03