New Posts  All Forums:Forum Nav:

Stupid math question

post #1 of 15
1/3/09 at 10:21pm
Thread Starter 

New question:

http://www.head-fi.org/forum/thread/397431/stupid-math-question-answered-thanks#post_6808613

 


Edited by Sduibek - 7/26/10 at 3:14pm
Reply
post #2 of 15
1/3/09 at 10:23pm
I'm afraid the answer is yes.
Reply
post #3 of 15
1/3/09 at 10:30pm
If order matters, i.e. ABCX and ABXC are considered different, you have 6 nPr 4 choices or 360 permutations.

If order does not matter (ABCX and ABXC are considered the same thing) there are 6 nCr 4, or 15, combinations.

Edit: Many calculators have the buttons to do this, I've seen a $5 Casio with stat functions. I used my nspire CAS in this case, it was close by.
Reply
post #4 of 15
1/3/09 at 11:19pm
What MCC said

Permutation and how it works
Reply
post #5 of 15
1/4/09 at 3:48am
Fairly simple, but one would need to know if order mattered.
Reply
post #6 of 15
1/4/09 at 4:22am
Oh you don't need a calculator! Both ways are ez to do in your head.

Order counts (permutations):

clearly 6x5x4x3 = 30 x 12 = 360

Order does not count (combinations):

6 choose 4 = 6 choose 2 (the 2 you didn't choose) so that's

6x5 / 2x1 = 30/2 = 15
Reply
post #7 of 15
1/4/09 at 4:34am
Here's another way to do the second problem (order does not count) in your head: A given set of four choices can be arranged 4! or 4x3x2x1 = 24 ways. So, to turn the 360 value in to the right answer, simply divide by 24.

360 / 24 = half of 360/12 or half of 30 = 15.

And now we have a complete proof of the result, from first principles with no need to have learned permutations/combinations.

To pick 4 of the 6, with order mattering, is clearly done this way: 6 choices, then 5 choices, then 4, then 3 or (as in my prior post) 6x5x4x3 = 360.

Then if order matters, clearly we have over-counted 4x3x2x1 (the possible ways to order 4 things, using the same logic as the last sentence) = 24, so divide 360 by 24 to get the answer 15.
Reply
post #8 of 15
1/4/09 at 5:17am
by my calculations, the answer is 42
Reply
post #9 of 15
1/4/09 at 5:41am
!
Reply
post #10 of 15
1/4/09 at 12:09pm
Thread Starter 
Quote:
Originally Posted by digger945 View Post
I'm afraid the answer is yes.
You just said the same thing in the RIAA thread. Stop trolling.
Reply
post #11 of 15
1/4/09 at 12:22pm
Thread Starter 
Quote:
Originally Posted by MCC View Post
If order matters, i.e. ABCX and ABXC are considered different, you have 6 nPr 4 choices or 360 permutations.

If order does not matter (ABCX and ABXC are considered the same thing) there are 6 nCr 4, or 15, combinations.

Edit: Many calculators have the buttons to do this, I've seen a $5 Casio with stat functions. I used my nspire CAS in this case, it was close by.
Quote:
Originally Posted by Dzjudz View Post
Quote:
Originally Posted by wavoman View Post
Oh you don't need a calculator! Both ways are ez to do in your head.

Order counts (permutations):
clearly 6x5x4x3 = 30 x 12 = 360
Order does not count (combinations):
6 choose 4 = 6 choose 2 (the 2 you didn't choose) so that's
6x5 / 2x1 = 30/2 = 15
Thank you!! My question has been answered and you didn't even make me feel more dumber than I already been. Thanks



Quote:
Originally Posted by demoNMaCHiN3 View Post
by my calculations, the answer is 42
I think you were guessing, but that is a very wise and educated guess indeed.
Reply
post #12 of 15
1/4/09 at 5:56pm
I wasn't guessing :P. I asked google: the answer to life the universe and everything - Google Search
Reply
post #13 of 15
7/26/10 at 3:12pm
Thread Starter 

What about if we have three columns of data, and each time will pick one selection from each column, and order does NOT matter?  I suck at math, good thing i'm going back to school this year.

 

For example we have:

headfi sorry try
is about to
a your enjoy
web wallet the
site   simpler
with   things 
a   in
forum   life
    as
    well
    ok?

 

Now, what makes this a little more complicated that it first appears, is that a combination of just Column A + Column B is valid.  For example, these would be valid:

web wallet

a sorry

headfi your

 

Column A + Column C will never happen, don't include such combinations in the calculations:

forum ok?

is the

 

Finally, the simplest version of this kind of calculation is valid, in addition to the A+B combo:

headfi sorry try

forum about life

a wallet enjoy

 

I believe if the last of the three "types" above were used (A+B+C) then I simply multiple the number in each column, right?  so i'd multiple 8 x 4 x 11 which = 352 possible outcomes.  What about when we add A+B to that though?  Would I simply then do 8 x 4 and add it, giving a grand total of 384?


Edited by Sduibek - 7/26/10 at 3:15pm
Reply
post #14 of 15
7/26/10 at 3:28pm

Yep.

Reply
post #15 of 15
7/26/10 at 3:38pm
Thread Starter 

Yay, I know stuff!  Man this is crazy, I got to pre-Calc in high school, and now I can't even do basic algebra without straining my headmuscles.  Amazing what seven years of not doing serious or regular math does to your brain ;)

 

This Is Your Brain On Leisure

Reply
New Posts  All Forums:Forum Nav:
  Return Home