Question 333643
Add their rates of working to get the rate that they work together
In words:
(part of the house Joe can paint)/(time it takes to paint it)
plus
(part of the house his Father can paint)/(Father's time to paint it)
equals
(One house painted)/(Their time working together to paint one house) 
Given:
Joe's rate of painting:
{{{1/6}}} (the {{{1}}} means one house)
Father's rate of painting:
{{{1/12}}}
--------------------
{{{1/6 + 1/12 = 1/t}}}
Multiply both sides by {{{12t}}}
{{{2t + t = 12}}}
{{{3t = 12}}}
{{{t = 4}}} days
It takes them 4 days working together