An unbiased coin is tossed. If the result is a
head, a pair of unbiased dice is rolled and the number obtained by adding the
numbers on two faces is noted. If the result is a tail, a card from a
well-shuffled pack of 11 cards numbered 2, 3, 4, ...,
12 is picked and the number on the card is noted. What is the probability
that the noted number is either 7 or 8?