# GMAT Math Practice - Speed Time Races

Concept: Average speed.

This GMAT quant practice question is from rates - speed, distance, and time. Concept covered: computing average speed of travel.

#### 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?

1. 60 mph
2. 56.67 mph
3. 53.33 mph
4. 64 mph
5. 66.67 mph

Average speed of travel = $$frac{\text{Total distance travelled}}{\text{Total time taken}}\\$ 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 = $\frac{\text{Total distance travelled}}{\text{Total time taken}} = \frac{320}{5}\\$ = 64 miles per hour. Choice D is the correct answer. Note: If Steve had traveled equal amount of time at 40 mph and 80 mph, his average speed will be the arithmetic mean$or simple average) of the two speeds. 