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Factorial question (is this enough characters yet?)?
10! / 6!(10-6)!=210
My question is, how was this answer arrived at? I can't find factorials on my TI-84 nor can it seem to handle those numbers anyway.
3 Answers
- Empire539Lv 78 years agoFavorite Answer
For reference, the factorial symbol ! can be found under [Math] > Prb > 4:!.
10! / (6!4!)
= 10 × 9 × 8 × 7 / (4 × 3 × 2 × 1)
= 5040 / 24
= 210
- AngelosLv 58 years ago
You don't need a calculator.
Write out the factorials. You get a fraction like this:
10*9*8*7*6*5*4*3*2*1
----------------------------
6*5*4*3*2*1 * 4*3*2*1
The factors 6*5*4*3*2*1 upstairs and downstairs cancel,
and you are left with
10*9*8*7 / 4*3*2*1
8 in the numerator cancels out with 4*2 in the denominator
and you are left with 10*9*7/3 = 10*3*7 = 210.
(In general, n!/m! = n*(n-1)*(n-2)*...*(n-(m-1)), which is easier to calculate.
E.g. 10!/6! = 10*9*8*7)
