21\frac{\sum_{r=2}^{n}\binom{n}{r}}{2^n} = \frac{2^n-n-1}{2^n}
What is the probability that if a fair coin is tossed n times we will get at least two heads?
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3 Answers
71Or P(at least two heads)= 1 - P (getting no head or 1 head)
