Question: Joe drives 120 miles at 60 miles per hour, and then he drives the next 120 miles at 40 miles per hour. What is the average speed for the entire trip in miles per hour?

1. 42
2. 48
3. 50
4. 54
5. 56

Answer:
Approach Solution (1):
As we know that:
Average speed = Total distance traveled / Total time taken
Joe drives 120 miles at 60 mph
Therefore, time taken by Joe =\({120\over60} = 2hours\)
He drives the next 120 miles at 40 mph. Therefore time taken by Joe =\({120\over40} = 3hours\)
Total distance traveled by Joe = 120 + 120 = 240 miles and
Total time taken = 2 + 3 hours
Average speed =\({240\over5} = 48mph\)

Correct option: B

Approach Solution (2):
Since the distance traveled in both cases is the same:
Average speed =\(\frac{2*60*40}{(60+40)}=\frac{4800}{100}=48mph\)
If the same distance traveled at ‘x’ mph and at ‘y’ mph
Then
Average speed =\(\frac{2xy}{(x+y)}\)

Correct option: B

Approach Solution (3):
\(t_1=\frac{120}{60}=2hours \\ t_2=\frac{120}{40}=3hours \\ T=t_1+t_2=5hours\)
Average speed = Total distance / T = \(\frac{120}{5}=48mph\)

Correct option: B

“Joe drives 120 miles at 60 miles per hour, and then he drive the next 120 miles at 40 miles per hour. What is the average speed for the entire trip in miles per hour?”- is a topic of the GMAT Quantitative reasoning section of GMAT. This question has been taken from the book “GMAT Official Guide Quantitative Review”. To solve GMAT Problem Solving questions a student must have knowledge about a good amount of qualitative skills. The GMAT Quant topic in the problem-solving part requires calculative mathematical problems that should be solved with proper mathematical knowledge.

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