A automotive test driver travels due north in a prototype hybrid vehicle at 30 mi/h for 2 hours. She then reverses her direction and travels due south at 60 mi/h for 1 hour.

What is the average speed of the vehicle?
a) 40 mi/h
b) 50 mi/h
c) zero mi/h
d) 60 mi/h
e) 30 mi/h

Option A. 40 mi/h

Explanation:

To obtain the average speed of the vehicle, we'll begin by calculating the distance travelled by the vehicle in each case. This is illustrated below:

Case 1:

Speed = 30 mi/h

Time = 2 h

Distance =...?

Speed = Distance /Time

30 = Distance /2

Cross multiply

Distance = 30 × 2

Distance = 60 mi

Case 2:

Speed = 60 mi/h

Time = 1 h

Distance =...?

Speed = Distance /Time

60 = Distance /1

Cross multiply

Distance = 60 × 1

Distance = 60 mi

Finally, we shall determine the average speed of the vehicle as follow:

Total distance travelled = 60 + 60

Total distance travelled = 120 mi

Total time = 2 + 1

Total time = 3 h

Average speed =..?

Average speed = Total Distance travelled /Total time

Average speed = 120/3

Average speed = 40 mi/h

Therefore, the average speed of the vehicle is 40 mi/h

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+15-35=-20

going in opposite directions