GMAT Quant Questions | GMAT Rates Q3

This sample GMAT Math question is an Average Speed problem solving question. The concept tested is to Compute the average speed of travel. An easy, GMAT 550 level time speed distance question.

Question 3: Jim travels the first 3 hours of his journey at 60 mph speed and the remaining 5 hours at 24 mph speed. What is the average speed of Jim's travel in mph?

1. 42 mph
2. 36 mph
3. 37.5 mph
4. 42.5 mph
5. 48 mph

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Video Explanation

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Explanatory Answer | GMAT Average Speed

Step 1 of solving this GMAT Rates Question: Compute total distance travelled and total time taken

Average speed Formula = \\frac{\text{Total Distance}}{\text{Total Time}})
If the time taken to travel the two parts is the same, the average speed formula = \\frac{a + b}{2}), where 'a' and 'b' are the speeds for the two parts.
If the distances covered at the two speeds is the same, the average speed formula = \\frac{2ab}{a + b}), where 'a' and 'b' are the speeds for the two parts.

In this question neither is the time same nor is the distance same for the two parts. So, we will use the original average speed formula.
Total distance traveled by Jim = Distance covered in the first 3 hours + Distance covered in the next 5 hours.
Distance covered in the first 3 hours = 3 × 60 = 180 miles.
Distance covered in the next 5 hours = 5 × 24 = 120 miles.
Therefore, total distance traveled = 180 + 120 = 300 miles.
Total time taken = 3 + 5 = 8 hours.

Step 2 of solving this GMAT Rates Question: Compute the Average Speed

Average speed = \\frac{\text{Total distance}}{\text{Total Time}} = \frac{300}{8}) = 37.5 mph.

Choice C is the correct answer.