Question 1083155
{{{1/20+1/12=3/60+5/60=8/60}}}, as if 8 driveways cleared in 60 minutes; or {{{4/3}}} driveways-worth cleared in 10 minutes.


The student will be late.  He needs 10 minutes to travel for being on-time to campus.  Time t, to clear the driveway by student and his brother combined will be   {{{(8/60)*t=1}}}
{{{t=60/8}}}
{{{t=15/2}}}
{{{t=7&1/2}}}------seven and a half minutes;
which leaves the student only 2.5 minutes of travel time before he will no longer be to campus on-time.