Brainteaser: Get in Gear - Answer

The number on each gear is the number of teeth it has. If you turn any one of the gears, the others also turn. The middle gear turns in the opposite direction of the other two gears.
The least common multiple of 25, 9, and 15 is 225. This is the point when all three gears will have made a whole number of complete turns and be back in their starting places.

So, for each gear, the number of turns is:

25 teeth — 9 turns
9 teeth — 25 turns
15 teeth — 15 turns

Copyright © 1996-2003 Houghton Mifflin Company. All Rights Reserved.
Available online at: http://www.eduplace.com/math/brain/7-359.html

For a better understanding of gears, play with the two gear exhibits in the Discovery Centre and have a look at the open gear box.

If you want to know more about gears go to:
How Gear Ratios Work
www.howstuffworks.com/gears.htm

Return to Brain Teaser Index