Question 487205
Add their rates of working
Joan's rate is ( 1 garden weeded) / ( 40 min )
Mother's rate is ( 1 garden weeded ) / ( 60 min )
Let their rate working together = ( 1 garden weeded ) / ( x min )
{{{ 1/40 + 1/60 = 1/x }}}
Multiply both sides by {{{ 120x }}}
{{{ 3x + 2x = 120 }}}
{{{ 5x = 120 }}}
{{{ x = 24 }}}
It will take them 24 min working together