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Discussion :: Chain Rule

1. 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:

2.  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 =$$\frac {6*21 } { 14 }$$

x = 9.

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