Question 736450
Add their rates of working
( 1 room / 9 hrs ) + ( 1 room / 10 hrs ) = 1 room / t hrs
{{{ 1/9 + 1/10 = 1 /t }}}
Multiply both sides by {{{ 90t }}}
{{{ 10t + 9t = 90 }}}
{{{ 19t = 90 }}}
{{{ t = 4.737 }}}
{{{ .737*60 = 44 }}}
Working together, it takes them 4 hrs and 44 min