Question 487066
n = 12
x = 5
p = .7
q = 1 - .7 = .3
p is probability of success
q is probability of failure
p(x) = nCx * p^x * q^(n-x)
for x = 5 and n = 12, this becomes:
p(5) = 12C5 * (.7)^5 * (.3)^7 which becomes:
p(5) = 792 * .16807 * .0002187 which becomes:
p(5) = .029111472


nCx is the combination formula of n! / (x! * (n-x)!))


the probabilities for x = 1 to x = 12 are shown below.


<pre>
p	0.7
q	0.3
n	12
x	p(x)
0	5.31441E-07
1	1.48803E-05
2	0.000190964
3	0.001485279
4	0.007797716
5	0.029111472   *****  p(x = 5)
6	0.079247896
7	0.158495792
8	0.231139696
9	0.239700426
10	0.167790298
11	0.071183763
12	0.013841287
	
	1             total probability equals 1 (as it should)
</pre>


this should be approximately equal to the probability found in your textbook.
if not, let me know what is in table 2 of appendix b in your notebook.