Question 481561
<pre>
A fair coin is tossed 7 times. What is the probability of obtaining exactly 4 heads?

Answer = {{{"C(7,4)"(1/2)^4*(1-1/2)^(7-4)

= (7!/(4!(7-4)!))(1/2^4)(1/2)^3 = ((7*6*5*4*3*2*1)/(4*3*2(3)!))(1/16)(1/2^3) =

((7*6*5*4*3*2*1)/(4*3*2(3*2*1)!))(1/16)(1/8) = 35/128 = .2734375  }}}

or you can get it on a TI-83 or 84 by

binompdf(7,1/2,4) 
ENTER

You get binompdf( by pressing 2ND VARS scroll down to binompdf(  
then press ENTER

You'll get the same answer .2723275.

Edwin</pre>