Answer:
4 mph
Step-by-step explanation:
Average speed is total distance over total time.
If you run for 0.4 hours at 7 mph, the distance you run is:
d = rt
d = (7 mi/hr) (0.4 hr)
d = 2.8 mi
If you walk for 0.8 hours at x mph, the distance you run is:
d = rt
d = (x mi/hr) (0.8 hr)
d = 0.8x mi
So your average speed is:
5 mi/hr = (2.8 mi + 0.8x mi) / (0.4 hr + 0.8 hr)
5 mi/hr = (2.8 mi + 0.8x mi) / 1.2 hr
6 mi = 2.8 mi + 0.8x mi
3.2 mi = 0.8x mi
x = 4
You should walk at 4 mph.
