Find the faulty machine
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A factory manufacturing flywheels for racing cars has ten machines to make them. The manufacturer knows the correct weight for a flywheel.
However, one day one of the machines begins to pro-duce faulty parts—either overweight or underweight.
How can the manufacturer find the faulty machine in only two weighings?
The manufacturer must take one flywheel made by each machine, find their total weight and compare this with the weight of the equivalent number of good flywheels to obtain the difference. Then he must take 1 flywheel from machine number one, 2 flywheels from machine number two and so forth, and weigh these against the correct weight for that number of parts
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