Question 617160
Add their rates of working
person 1: ( 1 house ) / ( 12 hrs )
person 2: ( 1 house ) / ( 15 hrs )
Let {{{ t }}} = the time in hours for them
to clean house together
{{{ 1/12 + 1/15 = 1/t }}}
Multiply both sides by {{{ 60t }}}
{{{ 5t + 4t = 60 }}}
{{{ 9t = 60 }}}
{{{ t = 6.667 }}} hrs
Note that {{{ .667 }}} hrs is {{{ 40 }}} min
Working together, it takes them 6 hrs and 40 min