posted by Will .
If it takes 4 people 20 days to build a house, how long does it take 6 people. I know the answer is 15 days, but for the life of me I can't figure out the formula for it.
20 days are required for 4 people to build a house. So it takes 4*20=80 man-days.
If we have 6 people, then it should take 80/6=13.3 days to finish the house.