Which expression represents the number of possible combinations of n items taken rat a time? n!
(n-nin
n!
(n-
(n-1)!
n!
(n-1)!!
n!

nCr = n! / (r!)(n-r!).

Step-by-step explanation:

That would be nCr = n! / (r!)(n-r!).                                                                               A quick way of working these out is as follows:                                                                                 Take 7C4:                                                                                                                                           this is 7*6*5*4/4*3*2*1  Cancelling out the 4 and 3*2: = 7*5  = 35                                                    15C12 = 15C(15-12) = 15C3 = 15*14*13 / 3*2*1 = 5*7*13 = 455.  

the answer   is 200

step-by-step explanation:

this is a problem about poisson probabilities.   i don't know if you've

already studied poisson distributions, or if you have a place to look

to read more about the subject.  

here's how you can see a poisson distribution coming.   when there are

a lot of events that may happen at any time (or any place), and when

you're counting how many of them happen at a particular time (or a

particular place), and each event is independent of the others, then

the result is a poisson distribution.   this is roughly true for the

chocolate chips; one chip being in a cookie has only a small effect on

the probability that another chip will be in the cookie.

once you know you have a poisson distribution, you know a lot.   there

is only one parameter to a poisson distribution, so if you know the

mean, you know everything.   the form of the distribution is

  probability of n chips = {[e^(-x)]*(x^n)} / (n! )

you bought 31 v bucks

step-by-step explanation:

25+6=31