A person has 5 coins in his pocket. Two have both sides being
heads, one has both sides being tails, and two are normal. The
coins cannot be distinguished unless one looks at them.
a) The person closes his eyes, picks a coin from pocket at
random, and tosses it. What is the probability that the down-side
of the coin is heads?
b) He opens his eyes and sees that the up-side of the coin is
heads. What is the...