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In the permutations of n things r, taken...

In the permutations of n things r, taken together, the number of permutation in which m perticular things occur together is `""^((n-m))P_((r-m))xx""^rP_m.`

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The correct Answer is:
`""^((n-m))C_r-mxx (r-m+1)!xx m!`
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