Mr. X completes 30 km of a journey at 6 km/hour and the remaining 40 km of the journey at 5 hours. His average speed for the whole journey is

Appeared in: RRB Staff Nurse Ahmedabad-2015

Explanation

The fundamental formula for average speed is Total Distance divided by Total Time.
First, calculate the time for the initial part of the journey: Time = Distance / Speed = 30 km / 6 km/hr = 5 hours.
Next, sum the distances and times for both parts of the journey. Total Distance = 30 km + 40 km = 70 km. Total Time = 5 hours + 5 hours = 10 hours.
Finally, apply the average speed formula: Average Speed = 70 km / 10 hours = 7 km/hr.

Option A: This value (70/11) likely comes from incorrectly adding a speed value (6 km/hr) and a time value (5 hours) in the denominator, which is dimensionally incorrect.
Option C: This value (7.5 km/hr) is an arithmetic error. It does not correspond to the correct calculation of Total Distance / Total Time.
Option D: This is the speed of only the second part of the journey (40 km / 5 hours = 8 km/hr), not the average speed for the entire trip.

Visual 1: Flowchart: A flowchart illustrating the step-by-step process: 1. Calculate Time1. 2. Identify Time2. 3. Sum distances (D1+D2). 4. Sum times (T1+T2). 5. 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.
While not a clinical question, this problem tests basic mathematical and analytical skills, which are essential for nurses.
Nurses frequently use similar calculations for medication dosages, IV drip rates, and intake/output monitoring, where accuracy is critical for patient safety.
What if? If the second part of the journey was 40 km at 8 km/hr instead of for 5 hours, the time for the second part would still be 5 hours (40km / 8km/hr), and the average speed would remain the same (7 km/hr).

How to Approach the Question

First, identify the core question: you need to find the 'average speed' for the 'whole journey'.
Recall the formula for average speed: Average Speed = Total Distance / Total Time.
Break the problem into its parts. Part 1: 30 km at 6 km/hr. Part 2: 40 km in 5 hours.
Calculate the missing information needed for the formula. For Part 1, you have distance and speed, so calculate the time: Time = 30/6 = 5 hours.
Sum the totals: Total Distance = 30 km + 40 km = 70 km. Total Time = 5 hours (from Part 1) + 5 hours (given for Part 2) = 10 hours.
Perform the final calculation: Average Speed = 70 km / 10 hours = 7 km/hr.

Concept Tested & Keywords

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