Question

A certain number of men can finish a piece of work in 10 days. If however there
were 10 men less it will take 10 days more for the work to be finished. How many men
were there originally?


(A) 110 men

(B) 130 men

(C) 100 men

(D) none of these

Answer 1

let m = the original number of men
then
10m = the number of man-days required to complete the job
:
"If there were 10 men less, it will take 10 days more for the work to be finished"
That means that it would take 20 days
20(m-10) = 10m
20m - 200 = 10m
20m - 10m = 200
10m = 200
m = 200/10
m = 20 men originally
:
:
Check this; find the number of man-hrs to do the job.
20*10 = 200 man-hrs (20 men working 10 days)
or
10*20 = 200 man-hrs (10 men working 20 days)