Posted by jen on Monday, September 27, 2010 at 9:30pm.
5 Doubles === 1 way
4 Doubles, 2 Singles === e.g. DDSSDD
number of ways = 6!/(2!4!) or C(6,4) = 15
3 Doubles, 4 Singles === C(7,3) = 35
2 Doubles , 6 Singles === C(8,2) = 28
1 Double , 8 Singles === C(9,1) = 9
10 Singles === 1
total = 89
...what?
i dont understand how its 89 ways!
how about 20 stairs, and N stairs? what would be the equation for that?
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