Question 562461
If 2 fair dice are rolled 15 times, what is the probability that (6,6) will appear only once?
<pre>
That's a binomial probability problem with n=15 trials.

The probability of a success [rolling (6,6)] is {{{1/36}}}. So we can do it 
by formula:

We want the probability of getting x=1 success out of n=15 trials, where
the probability of 1 success in 1 trial is p={{{1/36}}}, and the
probability of a failure in 1 trial is q = 1-p = 1-{{{1/36) = {{{35/36}}}  

The binomial probability formula is

C(n,x)p<sup>x</sup>q<sup>(n-x)</sup>

C(15,1){{{(1/36)^1(35/36)^(15-1)}}} = 

15{{{(1/36)(35/36)^14}}} = .2808706559 

You can also do it on a TI-84

Press ON
Press CLEAR
Press 2ND
Press VARS
Press ALPHA
Press MATH

On the newer versions you see this screen.
Type to make it look like this:

trials:15
p:1/36
x value:1
Paste

Use the down arrow key to hilite "Paste"

Press ENTER

You see

binompdf(15,1/36,1)  on the older versions you type to get that.

Press ENTER

Read .2808706559

Edwin</pre>