# Combinations from a repeting set

• Dec 9th 2011, 03:49 AM
dipsy34
Combinations from a repeting set
How many 10 long combinations can you make from the repeating set A = {a,b,c,d,e,f,g}

I was supposed to express this in factorials.
What confuses me is the fact that its a repeating set and how this affects the solution. I'm guessing that it would mean that 10 long combinations would look something like this: abcdefgabc,bcdefgabcd, cdefgabcde which would mean that the answer would be $10!/2*2*2$? since we always get 3 letters that goes in twice the combination.
• Dec 9th 2011, 04:09 AM
Plato
Re: Combinations from a repeting set
Quote:

Originally Posted by dipsy34
How many 10 long combinations can you make from the repeating set A = {a,b,c,d,e,f,g}

This is too vague to know what is to be counted. If we select ten from that set at least one letter is repeated up to four times.

• Dec 12th 2011, 05:15 PM
HallsofIvy
Re: Combinations from a repeting set
What do you mean by "repeating" set? You say "the repeating set {a, b, c, d, e, f, g}" but there are no "repetitions" in that. Do you mean, for example, that "a" and "b" might represent the same object?
• Dec 17th 2011, 07:58 AM
vincisonfire
Re: Combinations from a repeting set