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0 / 60 seg.
A man has 53 socks in his drawer: 21 identical blue, 15 identical black and 17 identical red. The lights are fused and he is completely in the dark. How many socks must he take out to be 100 percent certain he has a pair of black socks?
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Clue
FIVE. THERE ARE ONLY FOUR COLORS, SO FIVE SOCKS WILL GUARANTEE THAT TWO WILL BE THE SAME COLOR
40 SOCKS. IF HE TAKES OUT 38 SOCKS, ALTHOUGH IT IS VERY UNLIKELY, IT IS POSSIBLE THEY COULD ALL BE BLUE AND RED. TO BE 100 PERCENT CERTAIN THAT HE ALSO HAS A PAIR OF BLACK SOCKS HE MUST TAKE OUT A FURTHER TWO MORE SOCKS
YOU NEED TO TAKE OUT THREE SOCKS. TO HAVE A MATCHING PAIR, YOU NEED TO TAKE 2 SOCKS THAT ARE OF THE SAME COLOR. WHEN YOU TAKE 3 SOCKS, 2 OF THE SOCKS WILL BE OF THE SAME COLOR
YOU'D BE ASSURED OF A PAIR OF BLACK SOCKS BY PULLING 26 SOCKS. ALTHOUGH THE CHANCES ARE REMOTE, YOU JUST MIGHT PULL THE 24 BLUE SOCKS OUT FIRST. YOU'D NEED TWO MORE TO MAKE CERTAIN TO GET TWO BLACK SOCKS
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