A certain number of persons can complete a work in 90 days. If then, be 10 persons less, it would have taken 10 days more for the work to be completed. Find the total number of persons in the beginning.

100

Formula to be used here,

⇒ \( { M}_{1 } \) x \( { D}_{1 } \)  = \( { M}_{2 } \) x \( { D}_{2 } \)

where M = No. of men, D = No. of days.

⇒ Putting values in the formula,

⇒ M x 90 = (M - 10) x 100

⇒ M = 100 

Therefore, there were 100 men initially.