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Time & Work

Fourteen machines can produce 500 units in 12 hours. After four hours poduction, two more machines were started. How many hours will it take to complete the production of 500 units ?

Option:
A. 9
B. 5
C. 6
D. 7
Answer: D . 7

Justification:

In 12 hours, 14 machines can produce = 500 units.
In 4 hours , 14 machines can produce = (500 x 4) / 12 = 500 / 3 
Remaining units to be produced = 500 - 500/3 = 1000 / 3
Now, number of machines = 14 + 2 = 16
Next, 500 units are produced by 14 machines in = 12 hrs.
So, 1000 / 3 units shall be produced by 16 machines in
= (12 x 14 x 1000) / (500 x 16 x 3) = 7 hours

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