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Ten coins in five rows of four

geometryarrangementclassiclateral-thinking

You have ten coins.

Arrange them on a table so that there are five straight lines, each passing through exactly four coins. A coin may lie on more than one line.

Then: arrange nine coins so that there are eight rows of three.

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If every coin lay on only one line you would need twenty coins. So each coin must be on two lines. Think of a familiar figure with five lines, each crossing the other four.

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