Question 794213
So many people painting the room, best is to find the rate of 1 person to paint the room.  Then calculate what you want (or are asked).


Recognize, "paint the room" is 1 task.  One job.


3 people_______________4 hours______________1 job
(3/3)=1 people___________3*4 hours____________same 1 job


The one-person rate is 12 hours to do the job.  
You can express this as {{{1/12}}} jobs per hour, the one-person rate.


How much time for 2 people to do this one job?
The rates of each person is simply additive.
{{{highlight(2(1/12)*h=1)}}} corresponds to rate*hours=jobs and h is a variable for how many hours.


{{{highlight(h=6)}}}.
Six hours for two people to paint the room.





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Hopefully, you can intuitively understand that "(3/3)...." line above in the solution and discussion.