How Does This Math Problem Work?

[kermit911]

I am in a math class and I'm interested in how this works.

In brackets ( ) put a 12 at the top and a 4 under it with no line "this is not dividing", and that should equal 495. Why?

My teacher is horrible, I need to with draw from this class.

Thanks everyone
Kermit

[dr b]

that's computed as 12!/(8!)(4!) where ! represents factorial.

12! = 12 x 11 x 10 x ... x 1 = 479001600

8! and 4! computed similarly. and it does equal 495.

[dr b]

Explained here:

http://en.wikipedia.org/wiki/Combination

[kermit911]

I got it! I learned something! Woohoo

Here we go: 12! over 4!*8! = 495
So: 1*2*3*4.....*11*12 over "divided by"
1*2*3*4 "multiplied by" 1*2*3....*7*8
equals 495

Hope that help someone besides me :-)

[vascop]

If you want to avoid large numbers you can write
12!/8!=12 x 11 x 10 x 9
Now divide this by 4! gives
(12 x 11 x 10 x 9)/(4 x 3 x 2 x 1)
After cancelling this becomes
(3 x 11 x 5 x 3)=495

[jim360]

One of the most annoying parts perhaps of mathematics is the obscure and sometimes overlapping notation. Numbers in brackets arranged in a column means a vector to me, and when I do the 12!/8!*4! thing I would write 12C4 which means the same and avoids a clash. But notation is extremely tricky and even in the highest levels of mathematics there is often inconsistency over what things mean.