7 men can do a piece of work in 12 days. How many men will be required to do double the work in 8 days. Ans: 7 men can do the work in 12 days. 1 man can do the work in (7*12) = 84 days 1 man can do "double" the work - takes double the time - in (84*2) = 168 days So to complete 168 person-days of work in 8 days, you need (168/8) = 21 men. :)