Question 76116: A coin is tossed 9 times. What is the probability that the coin will land heads at least 7 times?
Found 2 solutions by stanbon, Edwin McCravy:
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! A coin is tossed 9 times. What is the probability that the coin will land heads at least 7 times?
It's a binomial problem with n=9, p=1/2, 7<=x<=9
Use"1- binomcdf(9,0.5,6)" on your TI calculator.
Ans:0.08984375...
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Cheers,
Stan H.
Answer by Edwin McCravy(20056)  (Show Source):
You can put this solution on YOUR website!
A coin is tossed 9 times. What is the
probability that the coin will land heads
at least 7 times?
This is a binomial probability. You can
find it directly from a binomial
table, a TI-83 calculator, or entirely
from the formula.
Using the formula:
gives the probability that in n trials
there will be exactly x successes
where
p = the probability of one success in
one trial and q = 1-p = the probability
of one failure in one trial.
In the case of a coin, p = 1/2 and q = 1 - 1/2 = 1/2
P(coin landing heads at least 7 times out of 9 tosses) =
P(coin landing exactly 7 times out of 9) +
P(coin landing exactly 8 times out of 9) +
P(coin landing exactly 9 times out of 9) =
 =
 =
Factor out 
 =
which gives the desired probability.
To calculate this we need:
Therefore the desired probability =
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If you use a TI-83 or TI-84 calculator, type in
1 - binomcdf(9,1/2,6)
then press ENTER and you get .08984375
To get binomcdf( , press 2nd, then VARS, then
scroll down to binomcdf( , then press ENTER.
Edwin
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