I just solved a multiple choice question but didn't get any of the answers. Let me know if I'm doing something wrong or if there is a mistake among the choices.
Given a standard playing card deck, what is the probability of being dealt 4 cards and getting exactly two differently ranked pairs?
There are 52C4 ways to be dealt 4 cards from a deck.
There are 13C2 ways to select two different ranks from which to make pairs.
In each of those ranks there are 4C2 ways to select pairs.
P(2 pairs) = [(13C2)(4C2)(4C2)]/[52C4] = 0.0104, rounded to 4 decimal places
The "nearest" choice was 0.021, which is, after rounding, exactly double my answer. I suspect this resulted from a similar looking calculation:
P(2 pairs) = [(13x12)(4C2)(4C2)]/[52C4] = 0.0207
The reasoning behind this would be: "There are 13 ways to select your first rank and 12 ways to select your second rank."
However, doesn't that calculation double count the ways we can select two different ranks?
The other answers were all greater than 0.04.
Thanks for any help!