Question 512436
In words:
The rate of the 2 painters together is:
( 1 fence ) / ( 4 hrs )
Let {{{ t }}} = the time for the experienced painter
to paint 1 fence, so his rate is:
( 1 fence ) / ( t hrs )
The inexperienced painter will take twice as long:
( 1 fence ) / ( 2t ) hrs
-----------------
I can add their rates of painting to get the rate
when they work together
{{{ 1/t + 1/(2t) = 1/4 }}}
Multiply both sides by {{{ 4t }}}
{{{ 4 + 2 = t }}}
{{{ t = 6 }}}
The experienced painter takes 
6 hrs to paint the fence alone