duahsolo wrote:

The rate of spin of a certain gyroscope doubled every 10 seconds from the moment a particular stopwatch started. If after a minute and a half the gyroscope reached a speed of 400 meters per second, what was the speed, in meters per second, when the stopwatch was started?

A) 25/3

B) 25/4

C) 25/8

D) 25/16

E) 25/32

This can be answered within a reasonable time frame by just charting each 10-second period.

- After 90 seconds: 400 meters/second

- After 80 seconds: 200 meters/second

- After 70 seconds: 100 meters/second

- After 60 seconds: 50 meters/second

- After 50 seconds: 25 meters/second

- After 40 seconds: 25/2 meters/second

- After 30 seconds: 25/4 meters/second

- After 20 seconds: 25/8 meters/second

- After 10 seconds: 25/16 meters/second

- START:

25/32 meters/second Answer: E

For more on this straightforward technique, see our free video -

http://www.gmatprepnow.com/module/gmat- ... /video/929Cheers,

Brent

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