arithmetic - a wheel that has 6 cogs is meshed with a larger wheel of 14 cogs when the smaller wheel has made 21 revolutions then the number of revolutions made by the larger wheel is - skillgun

Let the required number of revolutions made by larger wheel be x.
Then, More cogs, Less revolutions (Indirect Proportion)
=> 14 : 6 :: 21 : x 14 x x = 6 x 21
=> x = 6 x 21/ 14
=> x = 9.