You jog at 9.5km/hr for 8.0km, then you jump into a car and drive an additional 16km. With what average speed must you drive your car if your average speed for the entire 24km is to be 22km/hr?
The answer is 64km/hr, but I can't figure out how to get it

Question

You jog at 9.5km/hr for 8.0km, then you jump into a car and drive an additional 16km. With what average speed must you drive your car if your average speed for the entire 24km is to be 22km/hr?  
The answer is 64km/hr, but  I can't figure out how to get it

anonymous · Answer

First figure out how long it takes to jog the 8km by dividing the distance by the speed - you should get 0.84 hours. Next figure out how long the whole journey takes - 24 divided by 22 is 1.09 hours. The difference is 0.25 hours so you'll need to cover 16 km in 0.25 hours so the speed is 64km per hour (multiply both sides by 4). I hope this helps.