The question reads: A driver completed the first 20 miles of a 40-mile trip at an average speed of 50 miles per hour. At what average speed must the driver complete the remaining 20 miles to achieve an average speed of 60 miles per hour for the entire 40-mile trip? -assume that the driver did not make any stops during the 40 mile trip-
a. 65mph
b. 68mph
c. 70mph
d. 75mph
e. 80mph
Half the total distance is traveled at 50 miles per hour.
We can plug in ANY VALUE for the total distance, as long as half the total distance is traveled at 50 miles per hour.
Let the total distance = 300 miles.
Time to travel 300 miles at an average speed of 60 miles per hour = 300/60 = 5 hours.
Time to travel the first 150 miles at an average speed of 50 miles per hour = 150/50 = 3 hours.
Time remaining for the next 150 miles = total time - time for the first 150 miles = 5-3 = 2 hours.
To travel the next 150 miles in 2 hours, the required rate = 150/2 = 75 miles per hour.
The correct answer is
D.
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