Question 1006012
He can shovel the driveway in 16 minutes, and his brother claims to be able to do it in 12 minutes.
 If they shovel together, how long will it take to clear the driveway? 
:
let t = time for the two working together to clear the walk
let the completed job = 1 (a clear driveway)
:
A shared work equation, each will do a fraction of the work, the two fractions add up to 1
{{{t/16}}} + {{{t/12}}} = 1
multiply the equation by least common multiple of 16 & 12; 48, cancel and you have
3t + 4t = 48
t = 48/7
t = 6.9 min, so should be in good shape to make it to school.