Question 512647: A three-person maintenance crew could clean a certain building in 4 h, whereas a four-person crew could do the job in 3 h. If one worker of thecrew was an hour late, how long did the job? (Answer in decimal hours)
If it takes the 3-person crew 4 hours to do the whole job, then they can complete of the job in one hour. So when the 4th guy shows up, the now 4 person crew has of the job remaining. But a 4 person crew can do of the job per hour. So the question becomes: "How many s are there in ?" Divide. The 4-person crew takes 2.25 hours to complete.
My calculator said it, I believe it, that settles it