A person travels from town A to B at 40 km/hr, from B to C at 60 km/hr and returns from C to A at 30 km/hr. If the distances between A and B, B and C, and C and A are all equal, what is his average speed for the entire trip?

1. A

   42 km/hr

2. B

   38 km/hr

3. C

   40 km/hr

4. D

   36 km/hr

Appeared in: NCL (Northern Coalfields Limited)-NO

Explanation

• The core concept is that average speed is calculated as Total Distance divided by Total Time.
• Since the distances for all three segments of the journey are equal, we can assume a convenient distance (like the LCM of the speeds) to simplify calculations.
• The time for each segment is calculated by dividing the distance by the speed for that segment.
• Summing the time for all segments gives the total time of the journey.
• Dividing the total distance (3 times the segment distance) by the total time gives the average speed of 40 km/hr.

Why Other Options Were Wrong

• Option A: 42 km/hr is an incorrect result, likely due to an arithmetic error during the calculation of total time or the final division.
• Option B: 38 km/hr is incorrect. This value might be obtained by incorrectly averaging the speeds or making a calculation mistake.
• Option D: 36 km/hr is incorrect. This might result from a calculation error, such as incorrectly finding the sum of the time fractions.

Related Visual

• Visual 1: Flowchart: A visual flowchart illustrating the step-by-step process of calculating average speed: 1. Identify speeds and equal distance condition. 2. Assume a distance (LCM). 3. Calculate total distance. 4. Calculate time for each segment. 5. Calculate total time. 6. Divide total distance by total time.

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of Average Speed as background academic context rather than a clinical decision trigger.
• This question tests quantitative aptitude, a component of general intelligence sections in nursing entrance exams.
• Strong numerical and problem-solving skills are essential for nurses for tasks like medication dosage calculations, interpreting lab results, and managing patient data.
• What if the distances were not equal? If the distances were different (e.g., d1, d2, d3), you would calculate the time for each segment (t1=d1/40, t2=d2/60, t3=d3/30) and then use the formula: Average Speed = (d1+d2+d3) / (t1+t2+t3). The harmonic mean shortcut would not apply.

How to Approach the Question

• First, identify the key information: three different speeds (40, 60, 30 km/hr) and the crucial condition that the distance for each part of the journey is equal.
• Recognize that the formula for average speed is Total Distance / Total Time.
• To simplify the problem, assume a distance for each segment. The best number to choose is the Least Common Multiple (LCM) of the speeds (40, 60, 30), which is 120 km.
• Calculate the total distance traveled: 120 km × 3 = 360 km.
• Calculate the time taken for each segment using Time = Distance / Speed.
• Sum the times for each segment to get the total time.

Concept Tested & Keywords

• Concept Tested: Calculation of Average Speed
• Stem keywords: average speed, travels, km/hr, equal distances
• Lead-in keywords: what is
• Negative lead-in flag: false

Question ID

QwA2U5Ichrh4BBcqrh21vE

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