SOLUTION: suppose a fair coin is tossed 7 times. What is the probability of flipping exactly 2 heads?

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Question 293487: suppose a fair coin is tossed 7 times. What is the probability of flipping exactly 2 heads?
Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
suppose a fair coin is tossed 7 times. What is the probability of flipping exactly 2 heads?
That's a binomial problem.

%28nCx%29p%5Ex%2Aq%5E%28n-x%29

n = number of trials (tosses) = 7
x = number of successes required = 2
p = probability of one success in one trial (toss) = 1%2F2
q = 1-p = 1 - 1%2F2 = 1%2F2

%287C2%29%281%2F2%29%5E2%2A%281%2F2%29%5E%287-2%29
%287C2%29%281%2F2%29%5E2%281%2F2%29%5E5
%28%287%2A6%29%2F%282%2A1%29%29%281%2F2%29%5E7
%2842%2F2%29%281%2F%282%5E7%29%29
21%2F%282%5E7%29
21%2F128
0.1640625

Edwin