if you walk 1.5 hours at 3mph, how fast shoukd you run in the next 0.5 hours to have the average speed of 4mph
1.5 hr * 3 m/hr = 4.5 miles
(4.5 m + .5 hr * x m/hr ) / ( 1.5+ .5 hr) = 4 m/hr
4 .5 + .5x = 4 ( 2)
.5x = 3.5
x = 7 m/hr
+336 d=4*2 (1.5+0.5)
d=8 miles
8-4.5=3.5 miles to run in 0.5 hours
3.5=R*0.5
R=3.5/0.5=7 mph
So your answer is 7mph!
-wolfie ^-^
