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7 years, 11 months ago
7 years, 4 months ago
Hi Mutthu,
It say you have to choose r things from n things such that no two of them together. The same can be thought of in another way. Say you have r tings. So n-r are things are already arranged. If n-r things are arranged, there will be n-r+1 spaces. You can choose r spaces from these and put the 'r' things you have in those spaces. Thus the required ways will be n-r+1Cr
Hope that helps.
Thanks
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