Hello, is there any derivation on the net for the unordered with replacement formula?(adsbygoogle = window.adsbygoogle || []).push({});

I've searcced but didnt find any.

Ex: You have 5 different tickets and you shall choose 3 from a bowl. When one is chosen another like the chosen one is put in the bowl. The answer is 35, and the formula is

(n+r-1)!/r!/(n-1)!

The 35 possibilities are:

111 112 113 114 115 122 123 124 125 133 134 135 144 145 155

222 223 224 225 233 234 235 244 245 255 333 334 335 344 345 355

444 445 455 555

So please help me explain the formula (n+r-1)/Cr=(n+r-1)!/r!/(n-1)!

How do we come to this formula?

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# Unordered with replacement

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