Pick a card, any card. Better yet, pick 2!
Let's say I have a small deck of 4 cards. 2 black and 2 red. I shuffle this deck, place them face down, and ask you to pick any 2 cards. What is the probability that these card are the same color?
One person may say there are 3 possibilities. Both are black, both are red, or both are different colors. Therefore, the probability is 2/3.
Hold on! Says another person. That isn't right. They can both be black, both be red, the first card you picked is black and the other is red, or the first card you picked is black and the other is red. Thus, the cards match in 2 out 4 cases, giving us a probability of 1/2.
In fact, both are wrong!
What is the true probability and why?
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