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### Discussion :: Chain Rule

1. 3 pumps, working 8 hours a day, can empty a tank in 2 days. How many hours a day must 4 pumps work to empty the tank in 1 day?

2.  A. 9 B. 10 C. 11 D. 12

Answer : Option D

Explanation :

Let the required number of working hours per day be x.

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

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

 Pumps 4 : 3 :: 8 : x Days 1 : 2

4 x 1 x x = 3 x 2 x 8

x =$$\frac { (3*2*8) } { (4)}$$

x = 12.

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