A certain number of men can complete a job in 30 days. If there were 5 men more, it could be completed in 10 days less. How many men were in the beginning?

Answer: A. 10

Let x be the initial number of men; the total work is 30x (men x days).
With 5 more men ( x+5), the job takes 20 days, making the work 20(x+5).
Since the work is the same, 30x=20x+100, which simplifies to 10x=100.
Solving for x gives 10, so there were 10 men in the beginning.
Verification: 10 men X 30 days = 300 units. 15 men X 20 days = 300 units.

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