SOLUTION: it takes bob 10 hours to clean his room. It takes his mom 5 hours to clean his room. If bob starts cleaning at 1 pm and his mother starts helping at 2pm at what time will bob's roo

Question 908325: it takes bob 10 hours to clean his room. It takes his mom 5 hours to clean his room. If bob starts cleaning at 1 pm and his mother starts helping at 2pm at what time will bob's room be clean?
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
From 1 PM to 2 PM is 1 hr
------------------------
Bob's rate of cleaning is:
( 1 room ) / ( 10 hrs ) =
--------------------
The fraction of the room cleaned by
Bob in hr is:
of the room
-------------------------------
That means there is of the
room left to clean
-----------------
Add Bob's rate and his Mom's rate to
get their rate working together:
Let = time in hrs for them to
finish working together

Multiply both sides by

-------------
3 hrs after 2 PM is 5 PM
They will finish cleaning the room at 5 PM

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