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Question:

An unbiased coin is tossed eight times. The probability of obtaining at least one head and at least one tail is

127128

6364

255256

12

Solution:

p=P(H)=1/2,q=P(T)=1/2
P(at least one head one tail) =P(1≤H≤7)=1−[p(H)=0 and p(H)=8]=1−[2×(1/2)^8]=1−[2×1/256]=1−1/128=127/128.