A runner completes a 16 mile trip, running 8 miles uphill and 8 miles downhill in a total of 4 hours, if his uphill speed is 3 mph slower than his downhill speed, find his downhill speed.

Answer 1

add up the times
time = distance/speed

If his downhill speed is s,
8/s + 8/(s-3) = 4
s = 6

check:
8 miles @ 3mph = 8/3 hr
8 miles @ 6mph = 4/3 hr
total: 4 hr