Question

A fair coin is tossed 100 times. What is the probability that more than 55 heads are observed?

Answer 1

`P(A)=(100-55)/(100)=(45)/(100)=(9)/(20)`

Answer 2

Let us say T= probability of head turning up = 1/2 in one toss
H = probability of a tail turning up = 1/2 in one toss

Then P (56 heads or more) =
1/2^100 [ C(100,56) + C(100,57) + C(100,58) + ....
C(100,98) + C(100,99) + C(100,100) ]

where C(N, R) = N ! / [ (N - R)! R! ] number of occurrances of R formed from
N tosses.