If 40% of a number is added to 120, then the result is the same number. 30% of the same number is:

Appeared in: RRB Nsg. Superintendent-2026 (Shift -2nd)

Explanation

The problem is solved by first setting up an algebraic equation: Let the number be 'x'. The statement '40% of a number is added to 120, then the result is the same number' translates to 0.40x + 120 = x.
Solving this equation gives the value of the original number. Subtracting 0.40x from both sides results in 120 = 0.60x.
Dividing 120 by 0.60 gives x = 200. The original number is 200.
The final step is to calculate 30% of this number: 0.30 × 200 = 60.

Option B: 80 is 40% of the number (200), not 30%. This is a common error of miscalculating the required percentage.
Option C: 180 is 90% of the number (200). This value does not correspond to the 30% required by the question.
Option D: 90 is 45% of the number (200). This is an incorrect calculation.

Visual 1: Flowchart - A flowchart illustrating the step-by-step process: 1. Define variable 'x'. 2. Formulate the equation 0.40x + 120 = x. 3. Solve for x. 4. Calculate 30% of x. 5. Final Answer.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Solving a linear equation derived from a word problem involving percentages as background academic context rather than a clinical decision trigger.
While this is a mathematics question, strong numerical and analytical skills are essential in nursing for tasks like medication dosage calculations, interpreting lab results, and managing fluid balances.
Accurate calculation is critical for patient safety. A small mathematical error in a dosage calculation can have severe consequences.
What if the problem stated '40% of a number is subtracted from 120'? The equation would change to 120 - 0.40x = x, leading to a different result (x = 120 / 1.40 ≈ 85.7), demonstrating the importance of carefully reading and interpreting problem statements.

How to Approach the Question

First, identify the unknown quantity and assign a variable to it, for instance, 'x'.
Carefully read the word problem and translate the sentences into a mathematical equation. 'Percent of' means multiplication.
Solve the resulting linear equation for the variable 'x'.
Once 'x' is found, re-read the question to determine the final value that needs to be calculated (in this case, 30% of x).
Perform the final calculation and compare your result with the given options.

Concept Tested & Keywords

Concept Tested: Solving a linear equation derived from a word problem involving percentages.
Stem keywords: 40%, added to 120, result is the same number, 30% of the same number
Lead-in keywords: is:

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Practise the full RRB Nsg. Superintendent-2026 (Shift -2nd)

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