A man travels from point A to B at a speed of 55 km/h and returns to A through same route by increasing his speed by 50% of his earlier speed. His average speed (in km/h) for the whole journey is:

Appeared in: RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Explanation

First, calculate the return speed. The initial speed is 55 km/h, and it increases by 50% (27.5 km/h), making the return speed 55 + 27.5 = 82.5 km/h.
For a journey with two equal-distance segments at different speeds (v₁ and v₂), the average speed is calculated using the harmonic mean formula: Average Speed = (2 × v₁ × v₂) / (v₁ + v₂).
Substitute the speeds into the formula: (2 × 55 × 82.5) / (55 + 82.5).
This simplifies to 9075 / 137.5, which equals 66 km/h.

Option A: This is an incorrect result obtained from a miscalculation.
Option B: This value is close to the arithmetic mean of the two speeds ((55 + 82.5) / 2 = 68.75 km/h), which is an incorrect method for calculating average speed when times are unequal.
Option C: This is an incorrect result obtained from a miscalculation.

Visual 1: Diagram: A simple diagram showing a path from 'Point A' to 'Point B'. An arrow pointing from A to B is labeled '55 km/h'. A return arrow from B to A is labeled '82.5 km/h'. This visually represents the two legs of the journey with their respective speeds.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Average Speed for Equal Distances as background academic context rather than a clinical decision trigger.
This is a general aptitude question designed to test mathematical reasoning and problem-solving skills, which are part of the non-nursing syllabus for nursing entrance exams.
There is no direct clinical application for this specific type of average speed calculation in a nursing context.
What if? - If the stem changed one defining clue so that 66 no longer matched, reassess the option whose mechanism, classification, or indication now fits the revised presentation.

How to Approach the Question

First, identify the two different speeds for the two parts of the journey. The initial speed is given as 55 km/h.
Calculate the return speed by finding 50% of the initial speed and adding it to the original speed.
Recognize that since the distance for both parts of the journey is the same, you must use the harmonic mean formula for average speed: Avg Speed = (2 * v1 * v2) / (v1 + v2).
Avoid the common trap of calculating a simple average (arithmetic mean) of the two speeds, as this is only valid when the time traveled at each speed is equal.
Substitute the two speed values into the correct formula and solve for the average speed.

Concept Tested & Keywords

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Practise the full RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Attempt every question from this paper in a timed mock, then review the full solution for each one.