I need to know a way to derive the formula when doing combinations with repetitions.(adsbygoogle = window.adsbygoogle || []).push({});

THe formula is basically adapted from C(n;k) to

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

How is thing monster dervied?

i don't know if this will help, but the homework problem itself is:

How many distinguishable fruit baskets with 7 items can be created using apples, oranges, and pears?

I've used the formula to get an answer of 36. However, we haven't learned that formula in class, just the basic C(n,k) formula. Thats why I need to derive what I haven't learned in class from what I have learned.

I've looked at this thing for like 30 minutes and Im like nowhere. The n+k part of the numerator I think i get because its adding what we take away back to the set we are choosing elements from. I don't get the -1 though. or the rest.

Help!

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# Homework Help: Derivation of a formula

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