# Aptitude - Chain Rule - Discussion

### Discussion :: Chain Rule - General Questions (Q.No.9)

9.

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 mad by the larger wheel is:

 [A]. 4 [B]. 9 [C]. 12 [D]. 49

Explanation:

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.

 Prakash said: (Oct 17, 2010) Please explain another method for this problem.

 Avaneet said: (Aug 10, 2011) What is cogs?

 Rahul said: (Oct 7, 2011) Cogs = Tooth on the rim of gear wheel... If cogs increases , wheel circumference increases then revolution decreases dats means 6 cogs,less circumference,more revolution.. 14 cogs, more circumference ,less revolution compared to 6 cogs wheel cogs is inversely proportional to revolutions 6 cogs gives 21 revolution 1 cog will give =6*21 revolutions. 14 cog will give = 6*21/14=9

 Pankaj Kanaujiya said: (Jun 20, 2012) Lets firstly we take small cog..... 6 cog = 21 revolution 1 cog = 21*6 = 126 revolution now we have to find the revolution of 14 cog then 14 cog = 126/14 =63/7 = 9 hence answer is B. have a good day!!!

 Prasanna said: (Nov 3, 2015) Hi guys, If you think in another way it would be easy. Larger wheel has 14 cogs. Smaller has 6 cogs. So for one revolution of smaller wheel bigger will rotate 6/14. 1 revolution-----6/14. 21 revolution----21*6/14. And is 9.

 Anonymous said: (May 7, 2016) @Rahul. How is cogs inversely proportional to revolutions?

 Soundarya said: (Aug 21, 2016) @Anonymous. Because the given cogs are 6 which is less than that of the revolutions 2, which is more.

 Karthik said: (Jun 17, 2017) 21 is of small cog then why is it compared with lager ration?

 Sandeep said: (Sep 14, 2017) You can say 6 persons can do a piece of work in 21 days than in how many days 14 person can do the same work. 6*21 =14*x. =9.

 Sandeep said: (Sep 14, 2017) You can say 6 persons can do a piece of work in 21 days then in how many days 14 person can do the same work. 6*21 =14*x. =9.

 Vinay Vishwakarma said: (Feb 13, 2019) Which formula use for this question? please explain anyone.