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Jan 15, 2019 · 2. A box contains 10 black cards numbered 1 to 10 and 10 red cards numbered 1 to 10. In how many ways can we choose 10 out of the 20 cards so that there are exactly 3 matches where a match means a red card and a black card with the same number. My attempt: we can choose any 3 cards from red batch in (103) ( 10 3) ways and from the black batch ...
