Suppose there are three cards:
a black card that is black on both sides,
a white card that is white on both sides, and
a mixed card that is black on one side and white on the other.
All the cards are placed into a hat and one is pulled at random
and placed on a table.
The side facing up is black.
What are the odds that the other side is also black?
(In reply to D1? (spoiler)
by Steve Herman)
One could also argue that there only 2 cards with a black side, which is what we know from the chosen card.
Only 1 of those 2 is black on both sides => probability of black-black is 1/2.
Which equates to odds of 1:1.