182.Matching Socks from a Drawer
★★★classical probabilityCh. 1 — Classical Probability and Combinatorics444+ Problems in Probability
10 pairs of socks, each pair a distinct color, are in a drawer. You draw 2 socks at random. Find the probability that you obtain a matching pair.
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Condition on the first sock — how many of the remaining socks match it?
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