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Fig. 1 | Genome Biology

Fig. 1

From: What puzzle are you in?

Fig. 1

Four puzzles. a A mathematical jigsaw puzzle (Class I): How can you combine each of the numbers 2, 4, 6, and 8 with three different operations out of +, −, *, and / to arrive at the number 25? b A logical puzzle (Class II): This scale outputs one of three symbols, corresponding to “left is heavier,” “equal weights,” and “right is heavier.” While you can distinguish the symbols, you do not know their meaning. Find the four weighings that allow you to distinguish among 12 coins the one that is either slightly heavier or lighter than the rest. c A Class III puzzle: Add a mark to indicate that 3 of the meatballs have been eaten. d A Class IV puzzle: Can you connect the dots in a connected line with only 4 straight edges?

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