A wheel that has 5 cogs is meshed with a larger wheel of 15 cogs. When the smaller wheel has made 21 revolutions, the number of revolutions made by the larger wheel will be-

Question: A wheel that has 5 cogs is meshed with a larger wheel of 15 cogs. When the smaller wheel has made 21 revolutions, the number of revolutions made by the larger wheel will be-

Solution:

smaller wheel cross = 5 × 21 = 105 cogs by 21 revolutions.
so,
larger wheel will made = 105/15 = 7 revolutions.

Shortcut:
cogs of A : cogs of B = reolution of B : revolution of A
hense,
5 : 15 = X : 21
X = 7