Question 755342
Add the rate of filling and subtract
the rates of draining
Let {{{ t }}} = the time in hrs to drain the tank
{{{ -1/8 - 1/4 + 1/80 = -1/t  }}}
Note that the right side says that the result is a
rate of draining, not filling
Multiply both sides by {{{ 80t }}}
{{{ -10t - 20t + t = -80 }}}
{{{ -29t = -80 }}}
{{{ t = 80/29 }}}
{{{ t = 2.76 }}} hrs
{{{ .76*60 = 45.6 }}}
It will take 2 hrs and 45.6 min to drain the tank