QUESTION

How would you weigh a jet plane without using scales?

A traditional version of this interview brainteaser puzzle asks you to weigh an elephant without scales. Typically interview candidates will suggest looking up the specifications from Boeing’s website. Although it doesn’t hurt to offer this solution, the interviewer will push for alternatives.

ANSWER

The intended answer is that you taxi or fly the jet onto an small aircraft carrier, ferry, or other ship big enough to hold it. Paint a mark on the hull of the ship showing the water level. Then remove the jet. The ship will rise in the water.

Now load the ship with items of known weight (100 pound bales of cotton, whatever) until it sinks to exactly the line you painted on the hull. The total weight of the items will equal the weight of the jet.

If you’re more work-phobic than math-phobic, you can save effort by computing the volume of the ship between the two water levels, and multiplying that by the density of water. That too will give you the jet’s weight

Small aircraft carrier

Of course the aircraft carrier must be small enough so the water line actually moves!

 

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