Eight coins are tossed.
There are 8 trials.
These are binomial probabilities.
Use your TI-83 or TI-84
Find binompdf( and binomcdf(
by pressing 2ND then VARS then scroll down
with the down arrow key.
trials: 8
p: 0.5
x value: <--this changes (the number of heads (or tails) since
heads and tails have the same probability of 0.5
What is the probability that:
a. there is at least one tail?
This is the complement event of getting 0 tails,
so we subtract from 1:
1 - binompdf(8,0.5,0) ENTER
0.99609375
[Note: we can also consider this problem as getting
7 or fewer heads, or binomcdf(8,0.5,7), which gives
the same answer]
b. there are at least six heads?
This is the complement event of getting 5 or fewer heads
1 - binomcdf(9,0.5,5)
0.14453125
[Note: we can also consider this problem as getting
2 or fewer tails, or binomcdf(8,0.5,2), which gives
the same answer]
c. three or five heads come up?
These are exact values of x: so we use binompdf
binompdf(8,0.5,3)+binompdf(8,0.5,5)
0.4375
d. there are at least three heads?
1 - binomcdf(8,0.5,2)
0.85546875
[Note: we can also consider this problem as getting
5 or fewer tails, or binomcdf(8,0.5,5), which gives
the same answer]
e. two tails or four heads come up?
binompdf(8,0.5,2)+binompdf(8,0.5,4)
0.3828125
Edwin