Question

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

Answer 1

Let's denote amount of work as X, the number of men as Y, thus 1 man can do in one day& X/(10Y) of the total work. If there were 10 men less (Y-10) it will take 20 days to do all the work:
(Y-10)*20*& X/(10Y) =& X;
thus
(Y-10)/Y = 1/2
Y = 20.
Answer: there were 20 men originally.