sunilrawat wrote:Circular gears P and Q start rotating at constant speeds. Gear P makes 10 rev/min and Q makes 40 rev/min. How many seconds after the gears start rotating will Q have made exactly 6 revolutions more than P.
a. 6
b. 8
c. 10
d. 12
e. 15
D
When elements compete,
subtract their rates.
Rate for Q - Rate for P = 40-10 = 30.
Thus, every 60 seconds, Q makes 30 more revolutions than P.
Since Q needs to make 6 more revolutions than P, set up the following proportion:
30 revolutions/60 seconds = 6 revolutions/x seconds
x = 12.
The correct answer is
D.
Last edited by
GMATGuruNY on Tue Jul 12, 2011 6:42 am, edited 1 time in total.
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