Posted by Nerd101 on Tuesday, February 15, 2011 at 4:03am.
Runner runs 8 miles at 5 miles per hour, then another 2 miles at 7 miles per hour, find average speed.

Math  Reiny, Tuesday, February 15, 2011 at 10:07am
Average speed = total distance/total time
time for first leg = 8/5 hrs
time for 2nd leg = 2/7 hours
total time = 8/5 + 2/7 or 66/35
avg speed = 10/(66/35) = 10(35/66) = 5.3 mph