Question 723178
Add their rates of working
( 1 job ) / ( 3 hrs ) + ( 1 job ) / ( 4 hrs ) = ( 1 job ) / ( t hrs ) 
{{{ 1/3 + 1/4 = 1/t }}}
Multiply both sides by {{{ 12t }}}
{{{ 4t + 3t = 12 }}}
{{{ 7t = 12 }}}
{{{ t = 12/7 }}}
{{{ t = 1.7143 }}} hrs
{{{ .7143*60 = 42.86 }}}
Working together it will take them 1 hr and 43 min