SOLUTION: if a person takes 10 hours to clean his room. It takes his mother 5 hours to clean his room. If that person starts cleaning a 1pm and his mother starts helping at 2pm, at what ti

Question 548143: if a person takes 10 hours to clean his room. It takes his mother 5 hours to clean his room. If that person starts cleaning a 1pm and his mother starts helping at 2pm, at what time will it take the room to be clean?
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
First find the fraction of the room that
person cleans from 1 PM to 2 PM
Person's rate = ( 1 room ) / ( 10 hrs )

Person cleans 1/10 of the room in 1 hr
There is 9/10 of the room left to clean
-------------------------------
Add their rates.
Let = time for both to finish room
With person and Mother both cleaning:

Multiply both sides by

hrs
The room will be clean in hrs
4 hrs from 1 pm is 5 pm

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