Engineer's Puzzle

The Puzzle: 60 seconds puzzle – The great balls up!

Dave, the engineer, is a clumsy kind of fellow. Whilst walking around the factory floor one day, he turns and inadvertently knocks something over. When he turns around to see what he has done, he realises he's knocked a loose tungsten ball bearing in with some steel ones.

He looks down and sees nine bearings staring back at him. He knows there should only be eight, as they are prearranged ready for assembly. The problem is they're all the same size, and look exactly the same. He see's Charles Clutterbuck, the MD approaching, and not wanting to expose his clumsy ways, he comes up with a plan to right the situation quick sharp!

He grabs some old fashioned balancing weighing scales and making just two measurements isolates the tungsten bearing. He quickly puts it back in its rightful place, just in time to shake hands with Charles and pretend to be interested in his weekend.

Good old Dave.

So the question is, how did he do it? And can you beat Dave's time of just 60 seconds? Go!


The answer to this puzzle is simple. He makes three piles of three balls. Weights two piles against each other. He knows if they are equal the heavier tungsten is in the other pile, but if one is more than the other... well either way Dave is quickly down to three!

He now repeats the process, weighing two against each other. If they are equal, he knows the un-weighed ball bearing is tungsten, but if not, the heavier is obviously that troublesome bearing.

Too easy? Well, why not email your puzzles to me at and put your wits against the might of the Engineering Materials readership.

Justin Cunningham

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