A 3 maintenance crew could clean a certain building in 4 hours where as 4 person crew could the job in 3 hours if 1 worker of the 4 person crew was an hour late how long did the job take?

Considering that 1 person from the 4 person crew is late by 1 hour, the work is done for 1 hr by a 3 person crew. the 3 person crew completes 100% of the job in 4 hrs, hence, in 1 hr it completes 25 % of the job.

Now when 75% of the job is unfinished, the 4th member joins, so now it is a 4 person crew to do 75% of the job. If they can complete 100% job in 3hrs, they would complete the 75% job in 2.25 hrs (75x3/100).

Hence total time rquired for completion of the job = 2.25 + 1= 3.25 hrs ie 3 hrs 15 minutes.