A group of N people worked on a project. They finished 35% of the project by working 7 hours a day for 10 days. Thereafter, 10 people left the group and the remaining people finished the rest of the project in 14 days by working 10 hours a day. Then the value of N is
Let the unit of work done by 1 man in 1 hour and 1 day be 1 MDH unit (Man Day Hour).
Thus, in 7 hours per day for 10 days, the work done by N people =$$N\times\ 7\times\ 10$$ MDH units.
Since this is equal to 35% of the total work,
35% of the total work = $$N\times\ 7\times\ 10$$ MDH units.
Total work = $$\frac{\left(N\times\ 100\times\ 7\times\ 10\right)}{35}=200\times N$$ MDH units.
The work left = $$200N-70N=130N$$ MDH units.
Now, 10 people left the job. So, the number of people left = (N-10)
Since (N-10) people completed the rest of work in 14 days by working 10 hours a day,
$$(N-10)\times\ 14\times\ 10=130N$$
$$10N=1400$$
N = 140
Thus, the correct option is D.
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