A truck goes from Delhi to Bangalore at an average speed of 50 km/h. The journey takes 20 hours. It returns from Bangalore to Delhi on the same road at an average speed of 25 km/h. What was the average speed of the truck during the roundtrip?

1. A

   36 km/h

2. B

   36.33 km/h

3. C

   33.33 km/h

4. D

   33 km/h

Appeared in: UPUMS Nsg officer-2023

Explanation

• The fundamental principle for calculating average speed is to divide the total distance traveled by the total time taken.
• First, the one-way distance is calculated: 50 km/h × 20 hours = 1000 km. The total roundtrip distance is therefore 2000 km.
• Next, the time for the return journey is calculated: 1000 km / 25 km/h = 40 hours. The total time for the roundtrip is 20 hours + 40 hours = 60 hours.
• Finally, the average speed is the total distance divided by the total time: 2000 km / 60 hours = 33.33 km/h.
• A common error is to calculate the arithmetic mean of the speeds ( (50+25)/2 = 37.5 ), which is incorrect because the time spent at each speed is different.

Why Other Options Were Wrong

• Option A: This value does not result from the correct formula for average speed (Total Distance / Total Time). It is a calculation error.
• Option B: This value is also a result of an incorrect calculation and does not match the ratio of total distance to total time.
• Option D: This is an imprecise, rounded-down version of the correct answer. The exact calculation yields 33.333..., which is accurately represented as 33.33.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of average speed for a journey with varying speeds as background academic context rather than a clinical decision trigger.
• Although this is a mathematics question, the principle of precise calculation is fundamental in nursing for tasks like medication dosage, IV drip rate calculation, and fluid balance monitoring.
• Accuracy in calculations prevents errors that can have serious consequences for patient safety.
• What if? If the return journey was also completed in 20 hours (meaning the return speed was also 50 km/h), the average speed for the roundtrip would simply be 50 km/h, as the speed would be constant throughout.

How to Approach the Question

• First, identify all the given information: speed and time for the onward journey, and speed for the return journey.
• Recognize that the core formula needed is Average Speed = Total Distance / Total Time.
• Calculate the missing pieces of information: the one-way distance and the time for the return trip.
• Step 1: Calculate distance: Distance = Speed × Time (50 km/h × 20 h = 1000 km).
• Step 2: Calculate return time: Time = Distance / Speed (1000 km / 25 km/h = 40 h).
• Step 3: Sum the total distance (1000 + 1000 = 2000 km) and total time (20 + 40 = 60 h).

Concept Tested & Keywords

• Concept Tested: Calculation of average speed for a journey with varying speeds.
• Stem keywords: average speed, km/h, hours, roundtrip
• Lead-in keywords: What was

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