A wheel that has 6 cogs is meshed with a larger wheel of 18 cogs. When the smaller wheel has made 21 revolutions, then the number of revolutions mad by the larger wheel is: Options
A) 49
B) 4
C) 12
D) 7
E) 27
Let the required number of revolutions made by larger wheel be x.   Then, More cogs, Less revolutions (Indirect Proportion)   18 : 6 :: 21 : x 18 * x = 6 x 21   x =	(6 x 21)/18   x = 7.   Answer is 7.
<result>D</result>
A wheel that has 6 cogs is meshed with a larger wheel of 18 cogs. When the smaller wheel has made 21 revolutions, then the number of revolutions mad by the larger wheel is: