Let X denote the no. of coins showing 3 or more heads in a set of 7 coins X follows binomial distribution with n=7 p = probability of getting a head in a single toss of a coin ⇒p=
1
2
; thus q=1−p=
1
2
∴ Probability of getting at least 3 heads =P(x≥3) =1−P(x<3)