sammy can complete programming job in 8 hours alone. marilyn can complete programming job in 12 hours alone. how many hours would it take if sammy and marilyn work together

Answer 1

There speeds of doing the job separately are 1/8 per hour and 1/12 per hour. Assuming they are working on the same job together and not duplicating work, their combined speed is 1/12 + 1/8 = 5/24 jobs per hour.

The same assignment done together will take 1/(5/24) = 24/5 hours, which is 4 hours and 48 minutes.