Solution for #22

For starters, the answer is not 1/2. When the coin is drawn, there are four possibilities, each of which is equally likely:

The problem tells us that the last possibility did not occur. Therefore, there are three remaining possibilities, each of which is equally likely. Of the three, two of the possibilities will show heads on the other side; only one will show tails on the other side. So the probability that the other side of the coin is heads is two thirds.