If you run for 0.4 hours at 7 mph, how fast should you walk during the next 0.8 hours to have the average speed of 5 mph?
0.4 x 7 mph =2.8 miles - distance run.
Let the required speed =S
[2.8 + 0.8S] / [0.4+0.8] =5, solve for S
S =4 mph - must walk to attain an average of 5 mph, or:
6 miles / 1.2 hours =5 mph
+36916 .4 h * 7 m/h + .8 h * x m/h
_________________________
.4 + .8 hr = 5 m/h
2.8 + .8x = (1.2) 5
.8x = 3.2
x= 4 m/hr
