The pen weigh
The lemon, the apple and the plum weigh exactly the same as one coin, one key, one soldier and one pen.
How much does the pen weigh?
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The engineering department was arranging for a rather expensive catered lunch to bid farewell to their retiring colleague. They calculated that it would cost each person $30. One good mathematician remarked, "It's lucky that there aren't five fewer of us to split the...