pappueshwar wrote:hi all,
request to assist in solving the below problem:
A car travels from point A to point B. The average speed of the car is 60 miles/hr and it travels the first half of the trip at a speed of 90 mi/hr. What is the speed of the car in the second half of the trip?
A) 30
B)45
C)60
D)75
E)It cannot be determined from the information given.
If we understand how rates work, we can determine the correct answer here just by examining the answer choices.
If the SAME distance is traveled at two different speeds, the average speed for the whole distance will be JUST A BIT LESS THAN THE AVERAGE OF THE TWO SPEEDS.
To illustrate:
60 miles traveled at 20 miles per hour will take 3 hours.
60 miles traveled at 30 miles per hour will take 2 hours.
Average speed for the whole trip = 120/5 = 24 miles per hour -- JUST A BIT LESS THAN THE AVERAGE of 20 and 30.
The reason is that it will take MORE TIME to travel the distance at the slower speed, so the average speed for the whole trip will be CLOSER to the slower speed.
In the problem above:
The faster speed is 90.
The average speed for the whole trip is 60.
Of the answer choices -- which represent the slower speed -- only 45 is viable, since 60 is just a bit less than the average of 45 and 90:
(45+90)/2 = 62.5.
The correct answer is
B.
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