Question 721140
Assuming each person works at an equal rate, the rates are additive when they work together.  Let r be the rate at which any one worker works.  {{{3r*4=1}}}, or {{{3*4}}} is that one job in the 4 hour time period.  


{{{3r*4=1}}}
{{{3r*4/3=1/3}}}
{{{r*4=1/3}}}
{{{r*4/4=1/(3*4)}}}
{{{highlight(r=1/12)}}} The Rate of ONE worker.


How long for TWO workers together to do the job?  
Together , their combined rate is {{{1/12+1/12=1/6}}} jobs per hour, ... OR...
6 hours to paint the room (one job).