text: if it takes 10 people 12 hours to do a certain job, how many hours would it take 6 people, working at the same rate, to do 1/4 of the same job? man-hour required to do the job = 10*12 = 120 man-hour required to do 1/4 0f the job = 120/4 = 30 number of hours required to do 1/4 of the job by 6 people = 30/6 = 5 hrs.  i find this method of using man-hour useful.. you can also use a method called "unitary method".