25 men are employed to do a work in, which they could finish in 20 days but they drop off by 5 men at the end of every 10 days. In what time will the work be completed?
25 men x 20 days = 500 man-days to complete the job
at the end of 10 days they have completed 250 man days leaving 250 yet to be completed
in 10 more days they complete 20 x10 = 200 man-days leaving 15 men to complete 50 man -days of work
3 1/3 more days
10 days + 10 days + 3 1/3 days = ~ 24 days