Comments
Looking For Math Formula: Pairs
Written By Scrivs on Mar. 18, 2008.
10 Comments
Report Note
+ Clip This
I'm going under the excuse that it is 4:22am and my brain can't figure this out. What I am looking for is a formula that will tell me how many pairs I can make from a set of numbers.
For example if I have the numbers 1,2,3,4 then the possible pairs are:
- 1,2
- 1,3
- 1,4
- 2,3
- 2,4
- 3,4
I can see the pattern in my head, but can't devise a formula for some reason.
- Set of 2 = 1 pair
- Set of 3 = 3 pairs
- Set of 4 = 6 pairs
- Set of 5 = 10 pairs
- Set of 6 = 15 pairs
- Set of 7 = 21 pairs
- Set of 8 = 28 pairs
- Set of 9 = 36 pairs
- Set of 10 = 45 pairs
I know some genius here can pop out the formula for me.
Scrivs
Written Mar. 18, 2008 / Report /
Well I couldn't sleep till I got it and it really wasn't that hard (maybe the reason why I couldn't sleep. If n equals the total number in the set then formula is (n-1)*n/2. Pretty damn simple.
shadowsun7
Written Mar. 18, 2008 / Report /
I was actually thinking of a probability formula like 12P2, but then you up and solved it. You should be sleeping, Scrivs. ;P
Scrivs
Written Mar. 18, 2008 / Report /
I'm in one of my mythical work spurts.
joshawesome
Written Mar. 18, 2008 / Report /
I was helping my sister with her math homework last night. It took me four hours just to check her work and make sure she did it right. I haven't done any sort of trig in ten years, so it was a bit rough at first, but i figured it all out in the end.
RightOn
Written Mar. 18, 2008 / Report /
WOW!
This is your post > ---
This is my head > O
Scrivs
Written Mar. 18, 2008 / Report /
Ah come on it wasn't that bad, took me about 10 minutes and that is after realizing I originally messed up on the 8-10 sequence.
RightOn
Written Mar. 18, 2008 / Report /
You're talking to a guy who took College Algebra 3 times, and who probably uses the Calculator.app on his iPod Touch more than anyone else on the planet because he can't do basic 4 function math in his head.
Ozone42
Written Mar. 18, 2008 / Report /
There's probably a name for this. It's like a factorial subset.
touqen
Written Mar. 18, 2008 / Report /
I think you're looking for Combinations (or Binomial Coefficients).
http://mathworld.wolfram.com/Combination.html
I <3 mathworld.
Scrivs
Written Mar. 19, 2008 / Report /
Yeah I figured it was some type of combination, but had no idea the binomial coefficient stuff. That formula brings back nightmares of Probability class in college.