Per means one. So this asks for in one minute, and in one inch. 20 minutes = 6 inches. So dividing by 20 gets you one minute. 1 minute = 6/20 inches 1 minute = 3/10 inches 20 minutes = 6 inches. So dividing by 6 gets you one inch. 20/6 minutes = 1 inch 10/3 minutes = 1 inch
