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Speed, Time and Distance - December 16, 2003
The GMAT Sample Math question for the day is from the topic Speed, Time and Distance.
Question
Steve traveled the first 2 hours of his journey at 40 mph and the remaining 3 hours of his journey at 80 mph. What is his average speed for the entire journey?
A. 60 mph
B. 56.67 mph
C. 53.33 mph
D. 64 mph
E. 66.67 mph
The correct choice is (D) and the correct answer is 64 mph.
Explanatory Answer
Average speed of travel = 
Total distance traveled by Steve = Distance covered in the first 2 hours + distance covered in the next 3 hours.
Distance covered in the first 2 hours = speed * time = 40 * 2 = 80 miles
Distance covered in the next 3 hours = speed * time = 80 * 3 = 240 miles
Therefore, total distance covered = 80 + 240 = 320 miles
Total time taken = 2 + 3 = 5 hours.
Hence, average speed =  = 64 miles per hour.
Note: If Steve had traveled equal amount of time in each of the two speeds, then his average speed will be the arithmetic mean (or simple average) of the two speeds.
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