If a 13m long iron rod weighs 24.7kg, then what will be the weight of 6m long iron rod?

Appeared in: RRB Staff Nurse Kolkata-2015

Explanation

The problem states that the weight of an iron rod is proportional to its length. This is a direct proportion problem that can be solved using the unitary method.
First, calculate the weight of a single unit (1 meter) of the rod: 24.7 kg ÷ 13 m = 1.9 kg/m.
Next, multiply the weight per meter by the desired length to find the final weight: 1.9 kg/m × 6 m = 11.4 kg.

Option A: This value represents the weight of a 1-meter long rod (24.7 kg / 13 m = 1.9 kg), not a 6-meter long rod.
Option C: This value is incorrect and likely stems from a calculation error, such as incorrectly multiplying 1.8 by 6 instead of 1.9 by 6.
Option D: This value is incorrect and may be the result of a calculation error or transposing the digits of the correct answer (11.4 kg).

Visual 1: Infographic. A visual breakdown showing a 13m rod weighing 24.7kg, then isolating a 1m segment weighing 1.9kg, and finally showing 6 of these segments combined to weigh 11.4kg.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain This question tests the application of the unitary method and the concept of direct proportion in solving a word problem as background academic context rather than a clinical decision trigger.
While not a clinical question, this type of calculation demonstrates foundational numeracy skills essential for nursing.
Nurses use similar proportional calculations daily for tasks like medication dosage calculations, where the dose is adjusted based on patient weight or other factors.
What if the rod was made of a different material? The method would be the same, but the weight per meter (the constant of proportionality) would change, leading to a different final answer.

How to Approach the Question

First, read the question carefully to identify the given information: the length and weight of one rod (13 m, 24.7 kg) and the length of the second rod (6 m).
Recognize that the weight of the rod is directly proportional to its length. This means you can use the unitary method.
Step 1: Calculate the value of a single unit. In this case, find the weight of 1 meter of the rod by dividing the total weight by the total length.
Step 2: Use the unit value to find the required value. Multiply the weight of 1 meter by the new length (6 meters).
Double-check your arithmetic to avoid simple calculation errors.
Select the option that matches your calculated result.

Concept Tested & Keywords

Concept Tested: This question tests the application of the unitary method and the concept of direct proportion in solving a word problem.
Stem keywords: iron rod, 13m long, weighs 24.7kg, 6m long
Lead-in keywords: what will be the weight

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