Question

An unbiased coin is tossed thrice what is the probability of getting at least 2 heads

Answer 1

Answer:

1/2

Step-by-step explanation:

P(at least 2 heads)

= P(2 heads OR 3 heads)

= P(2 heads) + P(3 heads)

= $\binom32\times\frac18+ \binom33\times\frac18$

= 3/8 + 1/8

= 4/8

= 1/2

Alternatively:

By symmetry, P(at least 2 heads) = P(at least 2 tails)

But these events partition the sample space of all possible outcomes, so

P(at least 2 heads) + P(at least 2 tails) = 1

=> 2 × P(at least 2 heads) = 1

=> P(at least 2 heads) = 1/2