A certain number of men can finish a piece of work in 100 days. If there were 10 less men, it would take 10 days more for the work to be finished. How many men were there initially?

110

Assume initially there were "x" number menn for completing a work

X men completed the work in 100 days

x men one day work = 1/100

1 men one day work = 1/100x

if there were 10 men less, i.e. x-10

(x-10) men one day work = (x-10)/100x

Total number of days taken by (x-10) men = 100x/(x-10)

GIven that 10 less men would have taken 10 more days

Total number of days taken by (x-10) men= 110 = 100x/(x-10)

110x - 1100 = 100x

10x = 1100

x = 110 days

The correct answer is Option (4) → 110