posted by jawn on .
You jog at 6.6 mi/h for 5.0 mi, then you jump into a car and drive for another 5.0 mi. With what average speed must you drive if your average speed for the entire 10.0 miles is to be 10.4 mi/h?
answer is 24.5 mi/h.
let the speed in the car be x mph
so 5/6.6 + 5/x = 10/10.4
5/x = 10/10.4 - 5/6.6
5/x = .20396
x = 5/.20396
x = 24.5
he should drive the last 5 miles at 24.5 mph
if avg speed is 10.4 mph, then it took
10/10.4 hours or .9615 hours
time jogging = 5/6.6 = .7576 hours
time in car = 5/24.5 = .20408 hours
for a total time of .96166 hours
allowing for roundoff errors, close enough!