Two fair coins are tossed together. What is the probability that both land on heads? Give the probability as a fraction out of the four equally likely outcomes.

الشرح

The four equally likely results are heads-heads, heads-tails, tails-heads and tails-tails, and only one of them has heads on both coins, so one case in four succeeds. Counting the pair as though it could arise in two ways doubles the answer, because a result the two mixed pairs both produce would come out twice as large; two heads requires both coins to agree, and they agree on heads in a single case.