Question

Annie will toss a fair coin three times. What is the probability that all 3 tosses will result in heads?

Answer 1

P(at least one tail) + P(no tails) = 1
P(at least one tail) = 1 - P(no tails)
P(at least one tail) = 1 - (1/2)^3 = 1-(1/8) = 7/8

Answer 2

For a fair coin:
There are two possibilities, Head H or Tail T.
Total sample space = 2


Probability of Head = 1/2

Probability of Tail = 1/2

For all three tosses to be Head = (HHH)

P(HHH) = P(H) * P(H) * P(H)

= (1/2) * (1/2) * (1/2) = 1/8

Probability of 3 tosses been head = 1/8