A wheel that has 6 cogs is meshed with a larger wheel of 9 cogs. When the smaller wheel has made 21 revolutions, then the number of revolutions mad by the larger wheel is: Pick one.
A) 49
B) 4
C) 12
D) 14
E) 27
Let the required number of revolutions made by larger wheel be x.   Then, More cogs, Less revolutions (Indirect Proportion)   9 : 6 :: 21 : x 9 * x = 6 x 21   x =	(6 x 21)/9   x = 14.   Answer is 14.
<result>D</result>
A wheel that has 6 cogs is meshed with a larger wheel of 9 cogs. When the smaller wheel has made 21 revolutions, then the number of revolutions mad by the larger wheel is: