Question 1186711
8. You jog at 9.1 km/h for 5.0 km, then you jump into a car and drive an additional 13 km.
With what average speed must you drive your car if your average speed for the entire 18 km is to be 25 km/h?
:
let s = average speed in the car
:
Write a time equation, time = dist/speed
bike time + car time = total time
{{{5/9.1}}} + {{{13/s}}} = {{{18/25}}}
{{{5/9.1}}} + {{{13/s}}} = .72
multiply by 9.1s, cancel denominators
5s + 9.1(13) = 9.1s(.72)
5s + 118.43 = 6.552s
118.43 = 6.552s - 5s
118.43 = 1.552s
s = 118.43/1.552
s = 76.3  km/hr