A person traveling in a train counts 41 poles in two minutes. If the distance between two consecutive poles is 50 meters, what is the speed of the train (in km/hr)?

1. A

   120

2. B

   61.5

3. C

   60

4. D

   55

Appeared in: CGHS SSC - 2018

Explanation

• The core formula is Speed = Distance / Time.
• The total distance is determined by the number of gaps between the poles, not the number of poles. With 41 poles, there are 41 - 1 = 40 gaps.
• Total distance = 40 gaps × 50 meters/gap = 2000 meters, which is equal to 2 km.
• The time taken is 2 minutes, which is equal to 2/60 = 1/30 hours.
• Applying the formula: Speed = 2 km / (1/30 hr) = 60 km/hr.

Why Other Options Were Wrong

• Option A: This speed is double the correct answer. It would be correct if the time taken was only 1 minute (2 km / (1/60 hr) = 120 km/hr), which contradicts the problem statement.
• Option B: This is a common error that results from incorrectly using the number of poles (41) instead of the number of gaps (40) to calculate the distance. (41 poles × 50 m = 2050 m or 2.05 km; Speed = 2.05 km / (1/30 hr) = 61.5 km/hr).
• Option D: This value does not correspond to a logical calculation based on the given numbers and likely represents a random calculation error.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of speed from distance and time, involving unit conversion and logical problem-solving as background academic context rather than a clinical decision trigger.
• While not a clinical question, this problem tests attention to detail and logical reasoning, which are critical skills for nurses.
• Nurses must be precise in calculations, such as when determining medication dosages or IV drip rates, where a small error (like using 'n' instead of 'n-1') could have significant consequences for patient safety.
• What if? If the question stated the person counted '41 gaps' instead of '41 poles', the total distance would be 41 × 50 = 2050 meters. The speed would then be 2.05 km / (1/30 hr) = 61.5 km/hr, making option B correct. This highlights the importance of carefully reading the problem statement.

How to Approach the Question

• First, identify all the numerical values given in the problem: 41 poles, 2 minutes, 50 meters.
• Recognize the key logical step: The distance is measured by the gaps between the poles. For 'n' poles, there are 'n-1' gaps.
• Calculate the total distance by multiplying the number of gaps by the distance of one gap: (41 - 1) × 50 meters.
• Convert the units to match the desired output. Convert meters to kilometers (divide by 1000) and minutes to hours (divide by 60).
• Apply the standard formula: Speed = Distance / Time.
• Compare your calculated result with the given options to find the correct answer.

Concept Tested & Keywords

• Concept Tested: Calculation of speed from distance and time, involving unit conversion and logical problem-solving.
• Stem keywords: train, poles, minutes, distance, speed
• Lead-in keywords: what is the speed

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