Three boxes contain marbles. Box A has 5 red marbles. Box B has 5 blue marbles. Box C has 3 red and 2 blue marbles. All boxes are completely opaque and have incorrect labels matching their contents. You may blindly draw one marble from any box. Which box do you draw from to correctly identify the contents of all three boxes?
The box labeled 'Red and Blue'
Since all labels are wrong, the box labeled 'Red and Blue' cannot contain both red and blue marbles; it must contain either all red or all blue. Drawing one marble from it tells you its true contents, and by elimination you can fix the other labels.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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