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### Discussion :: Chain Rule

1. 39 persons can repair a road in 12 days, working 5 hours a day. In how many days will 30 persons, working 6 hours a day, complete the work?

2.  A. 10 B. 13 C. 14 D. 15

Explanation :

Let the required number of days be x.

Less persons, More days (Indirect Proportion)

More working hours per day, Less days (Indirect Proportion)

 Persons 30 : 39 :: 12 : x Working hours/day 6 : 5

30 x 6 x x = 39 x 5 x 12

x $$\frac { (39*5*12) } { (30*6) }$$

x = 13.

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