400 person working 9 hours per day complete 1/4 th of the work in 10 days. The number of additional persons, working 8 hours per day required to complete the remaining working in 20 days is

A 375

B 275

C 255

D 345

Correct Answer: Option B

Solution: Work done 1/4 th in 10 days. So work left 1- 1/4 = 3/4

1/4 th needs 10 days so 3/4 th need 30 days to complete

Now, 30 days need working 9 hours for = 400 persons

1 " " " 1 " " = 400 \( \times \) 30 \( \times \) 9

20 " " " 8 " " = 400 \( \times \) 30 \( \times \) 9 / 20 \( \times \) 8

= 675 persons

So, persons to be added 675 - 400 = 275