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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