# statistics exam on thrusday, me = stuck.

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#### joshd

##### Fully Optimized
Binomial Distribution

OK, how do I use the nCr key? google and my revision guide are yielding no clues...

so;
n=total number of... umm... trials is it?
r=number of the things you want...?

so if i wanted to do... i dont know. i can't even think of an example where i would use this at the moment.

any help would be appreciated. thanks.

#### Nubius

##### Golden Master
nCr key is used (I believe) when you have a problem that says something to the effect of:

"Suppose there is a committee of 12 people and you wanted to choose 3. How combinations of people can you pick?"

that was just on my math test, buuut since I took that over a week ago, I've already pushed most of it out of my head I'm pretty sure that's the way it goes though.

#### joshd

##### Fully Optimized
yea, thats the one.

so i just pop the total, nCr, then what i want, and it tells me the combinations.

there was also something we did once that involved:

nCr something something, that worked out something else, but i cant remember what it was...

#### Nubius

##### Golden Master
Dont know, believe you just gotta remember it by thinking the C is 'Choose' so it's like

12 people CHOOSE 3 kind of deal.

#### joshd

##### Fully Optimized
OK, so it is just the number of possible combinations? i get it now. thanks Nubius.

#### Chankama

##### Fully Optimized
Yup, it's the # of possible combinations. Inherently, this implies that order doesn't matter.

12C4 = From 12 distinct objects, how many groups of 4 can you make where order doesn't matter.

12P4 = Same as above, but order matters.

#### Nubius

##### Golden Master
yeah cause 12P4 would be the equivelant of doing 12x11x10x9 wouldn't it....so in the case of the P, if you hit 12P12 it'd be like doing 12x11x10 etc..etc..down to 1....but if the number is less than 12 then it'll just go down that many, so 12P4 would be what I just said above I think.

I believe that's what chankama is saying about order.

Holy crap, I was able to help with math before chankama!

I R TEH SMART!!! CHANKAMA R TEH....................STILL SMART!!!

#### diabloII

##### Fully Optimized
you're going to see at most 1 question about binom distribution on the test

if i were you i wouldn't even bother with it

what kind of stats exam are you taking?

#### joshd

##### Fully Optimized
GCSE statistics. well yea, there will be one question, but i need all the marks i can get really...

#### Nubius

##### Golden Master
theres nothing wrong with him simply wanting to know.

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