Final answer:
No, it is not possible for a truck to average 20 mi/hr for the first half of a round trip journey and still maintain an overall average speed of 40 mi/hr, as the time already spent traveling the first half would not allow for the needed average speed to be met.
Step-by-step explanation:
The question is asking whether it is possible for a truck making a round trip with an average speed of 40 mi/hr to have a speed of 20 mi/hr on the first half of the journey. To examine this scenario, consider that average speed is calculated by the total distance divided by the total time. Assuming that the truck travels 40 miles one way and 40 miles back, the total distance would be 80 miles. If the truck traveled at 20 mi/hr for the first half, it would take 2 hours to cover the first 40 miles. To maintain an average speed of 40 mi/hr for the entire 80 miles, the truck would need to cover the 80 miles in 2 hours total; however, it has already taken 2 hours for the first half.
Therefore, unless the truck's speed for the second half is infinitely fast, it is not possible for the truck to average 20 mi/hr on the first half and still maintain an overall average speed of 40 mi/hr for the trip. The answer is b. No, it is not possible.