Suppose that you flip a coin 15 times. What is the probability that you achieve
at least 4 tails?
Use your TI-83 or TI-84, the binomcdf( feature under 2ND VARS
The binomcdf( feature only calculates "at most", so if you want
the probability of "at least" you must convert it to "at most",
by subtracting from the number of trials, and subtract the
probability p of a success on one trial from 1.
At least 4 tails is the same as at most 11 heads.
So the number of trials is 15, the probability p of a head on one
trial is 0.5, and the x value is 11, so you want
binomcdf(15,0.5,11)
press ENTER and get
0.982421875
Edwin
