Question 770901
The job can be identified as 1 room, and you want a rate of 4/8 room per hour.  This is 1/2 room per hour rate.  The rate of 1 person or 1 friend is 1/10 room per hour.  


The objective is find how many friends including yourself will achieve a rate of at least 1/2 room per hour.  We assume the rates of all friends in the group of painters are additive.


{{{highlight(n*(1/10)=1/2)}}}
{{{n=10/2}}}
{{{n=5}}}
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The group must have 5 people to do the painting for the expected rate.