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 1600 meters per second, what was the speed, in meters per second, when the stopwatch was started?
Choose the most appropriate option
A) 25/3	B) 25/4	C) 25/8	D) 25/16	E) 25/32
Let x be the original speed when the stopwatch was started.   In 90 seconds, the speed doubled 9 times.   2^9 * x = 1600   x = (2^6 * 25) / 2^9 = 25/8   The answer is 25/8.
<result>C</result>
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 1600 meters per second, what was the speed, in meters per second, when the stopwatch was started?