The coin problem is said to be an interview puzzle for tech companies. Find other interview puzzles here. A similar puzzle to the coin riddle is a famous problem called the wine and water mixing problem. W. W. Rouse Ball, a British mathematician and fellow at Trinity College, Cambridge, wrote about the wine and water problem in 1982 in his book Mathematical Recreations and Essays. It reads: “One tumbler is half-full of wine, another is half-full of water: from the first tumbler a teaspoonful of wine is taken out and poured into the tumbler containing the water: a teaspoonful of the mixture in the second tumbler is then transferred to the first tumbler. As the result of this double transaction, is the quantity of wine removed from the first tumbler greater or less than the quantity of water removed from the second tumbler?” Solutions to this problem can be found here or here.

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