I found the following problem in Rosen's Discrete Mathematics and Its Applications 6th ed.:
There are three cards in a box. Both sides of one card are black, both sides of one card are red, and the third card has one black side and one red side. We pick a card at random and observe only one side.
If the side is black, what is the probability that the other side is also black?
Shouldn't the answer to the question be $1/3$, as among $3$ cards only $1$ of them has both sides black. But the book says answer is $2/3$, do I miss anything?