GeekDad Puzzle of the Week Answer: Gear Up

Reading Time: 2 minutes

Image: Flickr/avrene

Piaget’s developmental stages should certainly include mention of the age at which kids learn to build with Lego gears. And then the next stage would be understanding them. This week’s puzzle required both. Here it was:

“Combine the standard Lego gears of 8, 12, 16, 20, 24, 36 and 40 teeth in a functional gear train so that one rotation of an initial gear with 36 teeth results in 20 rotations of the final axle. You needn’t use all gears, but you can for style points. Accomplishing this with exactly five axles is worth two contest entries. (Hint: you may want to consider loading more than one gear onto each axle.)”

And — argh! — sorry for the ambiguity in the puzzle wording. Yes, of course you have to use more than one gear of certain sizes. If you discount the power of friction, there are an infinite number of workable solutions. However, one of the ideal, five-axle solutions is this:

1st axel – 36-tooth gear

2nd axel – 12-tooth gear & 16-tooth gear

3rd axel – 12-tooth gear

4th axel – 40-tooth gear & 16-tooth gear

5th axel – 8-tooth gear

This week’s winner of the $50 ThinkGeek gift certificate, randomly drawn from the correct entrants is… Erik! He writes that he’s a “First time reader, first time entrant, but I love puzzles, I love lego, and I think is awesome!” Actually, he didn’t include the final exclamation point. That was my edit. But we know he meant it.

The rest of us can use the code GEEKDAD93SF to save $10 at ThinkGeek on an order of $50 or more. Don’t forget to tune in Monday when Jud offers a non-ambiguous puzzle! Cheers.

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