Word Problems/Fred and Frank Problem
saladgirl70 wrote at 2012-11-29 16:03:04
The algebra is sound, but I disagree with the average rate of speed. Average speed is (Total Distance)/(Total Time). Frank's average speed is (walk speed + run speed)/2, while Fred's will be slower since he spends more time walking than running. To see this, try it with the following numbers: W=5 mph, R=10 mph, D=10 miles. Then Frank's time = 20/(15)= 1.33 hr. So his avg speed = 10 mi / 1.33 hr = 7.5 mph = (R + W)/2. While Fred's time = 1.5 hr. His avg speed = distance / total time = 10 mi / 1.5 hr = 6.67 mi/hr.