A wheel that has 6 cogs is meshed with a larger wheel of 7 cogs. When the smaller wheel has made 21 revolutions, then the number of revolutions made by the larger wheel is:	Options
A) 9 B) 10 C) 6 D) 18 E) 7
Explanation :   Let the required number of revolutions made by larger wheel be x.   Then, More cogs, Less revolutions (Indirect Proportion)   7:6::21:x =&gt; 7 * x = 21 * 6   =&gt; x = (21 * 6)/7   =&gt; x = 18   Answer : 18
<result>D</result>
A wheel that has 6 cogs is meshed with a larger wheel of 7 cogs. When the smaller wheel has made 21 revolutions, then the number of revolutions made by the larger wheel is: