Question 1140365
Add their rates of working and
let{{{ t }}} = their time working together
{{{ 1/30 + 1/10 = 1/t }}}
Multiply both sides by {{{ 30t }}}
{{{ t + 3t = 30 }}}
{{{ 4t = 30 }}}
{{{ t = 7.5 }}}
It takes 7 min 30 sec with both working