We have a rate of 3/5 of a wall in 40 minutes. What's the rate in walls per hour and hours per wall?
40 minutes is of course 2/3 hours.
(3/5 walls)/(2/3 hours) = (3/5)(3/2) walls per hours = 9/10 walls per hour
(2/3 hours)/(3/5 walls) = 10/9 hours per wall
Answer: 0.9 walls in 1 hours
