Question 554834
Add their rates of painting to get their 
rate working together
A's rate: ( 1 house ) / ( 4 hours )
B's rate: ( 1 house ) / ( 7 hours )
Let their time working together = {{{ t }}}
{{{ 1/4 + 1/7 = 1/t }}}
Multiply both sides by {{{ 28t }}}
{{{ 7t + 4t = 28 }}}
{{{ 11t = 28 }}}
{{{ t = 2.545 }}}
{{{ .5454*60 = 32.73 }}}
Working together, they paint the house in 2 hrs and 33 min