BTGmoderatorDC wrote:Vivian drives to her sister's house and back. She takes the exact same route both ways. On the trip out she drives an average speed of 50 miles per hour. On the trip back she drives an average speed of 70 miles per hour. What is her approximate average speed for the round trip in miles per hour?
A) 50
B) 58.3
C) 60
D) 61.7
E) 70
When the SAME DISTANCE is traveled at two different speed, the average speed for the entire trip will be just a little less than the average of the two speeds.
The reason:
The trip at the lower speed takes longer than the trip at the higher speed.
Since more time is spent at the lower speed, the average speed for the whole trip will be closer to the lower speed than to the higher speed.
Here, the average of the two speeds = (50+70)/2 = 60.
Thus, the average speed for the entire trip must be just a little less than 60.
The correct answer is
B.
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