Three identical-looking boxes contain colored balls: Box 1 has 2 Red balls, Box 2 has 2 Blue balls, and Box 3 has 1 Red and 1 Blue ball. Every box is currently labeled incorrectly as 'RR', 'BB', or 'RB'. You pull a single Blue ball from the box labeled 'RB'. What are the actual contents of the box labeled 'RR'?
1 Red ball and 1 Blue ball (RB)
Drawing a blue ball from 'RB' proves that box contains 'BB' (since 'RB' is a false label). The box labeled 'RR' cannot contain 'RR' (false label) nor 'BB' (already identified). Therefore, the box labeled 'RR' must actually contain 'RB'.
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: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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