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

Answer: Option B

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.

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