It takes Dustin 2 hours to shovel the snow from his driveway and sidewalk. It takes his sister 3 hours to shovel the same area. How long will it take them to shovel the walk if they work together?

Answer 1

Dustin = 1 driveways / 2 hours
sister = 1 driveway / 3 hours

Dustin + sister = ( 1/2 + 1/3)driveway / hours
= 3/6 + 2/6 = 5/6 driveways/hour
invert for 6/5 = 1 1/5 hours/ driveway