Answer:
Step-by-step explanation:
D
I am not sure if I did this the easiest way, but here's how I went about it.
40 miles/60 mph = average trip time
20 miles/50 mph = time it took to complete first 20 miles
20 miles/X mph = time it took to complete second 20 miles
therefore
40/60 hours = 20miles/50mph + 20miles/X mph.
Solved for X and you get 75
The drive must have an average speed of 70 miles per hour in the last 20 miles of the entire 40-mile trip. (Answer: C)
To determine the resulting Average Speed for the entire trip, we need to apply the concept of Weighted Average, whose expression for this case is presented below:
[tex]\bar v_{r} = \frac{x_{1}\cdot \bar v_{1} + x_{2}\cdot \bar v_{2}}{x_{1}+x_{2}}[/tex] (1)
Where:
[tex]\bar v_{r}[/tex] - Average speed for the entire trip, in miles per hour.
[tex]\bar v_{1}[/tex] - Average speed for the first 20 miles, in miles por hour.
[tex]\bar v_{2}[/tex] - Average speed for the last 20 miles, in miles per hour.
If we know that [tex]\bar v_{r} = 60\,\frac{mi}{h}[/tex], [tex]\bar v_{1} = 50\,\frac{mi}{h}[/tex] and [tex]x_{1} = x_{2} = 20\,mi[/tex], then we find the average speed for the last 20 miles of the 40-mile trip:
[tex]60\,\frac{mi}{h} =\frac{(20\,mi)\cdot \left(50\,\frac{mi}{h} \right) + (20\,mi)\cdot \bar v_{2}}{40\,mi}[/tex]
[tex]\bar v_{2} = 70\,\frac{mi}{h}[/tex]
The drive must have an average speed of 70 miles per hour in the last 20 miles of the entire 40-mile trip. (Answer: C)
For further detail, please see the following link to a related question: https://brainly.com/question/18554478
