Alvin can go upstream at a rate of 6 miles per hour and downstream at a rate of 12 miles per hour. One day while Alvin was on the river, he received a call telling him he needs to turn around and come home. So he turned around and went back to his starting point. If his entire trip took 12 hours, how far did he travel on the river?

Answer 1

since time = distance/speed,

d/12 + d/6 = 12