If 20% of an electricity bill is deducted, then Rs. 180 is still to be paid. What is the original bill?

Appeared in: RML 2023

Explanation

The problem states that after a 20% deduction, Rs. 180 is the remaining amount. This means Rs. 180 represents 80% (100% - 20%) of the original bill.
To find the original bill (which is 100%), we can set up the equation: 0.80 × Original Bill = 180.
Solving for the Original Bill by dividing the remaining amount by the remaining percentage (in decimal form) gives the correct answer: 180 ÷ 0.80 = 225.

Option A: If the original bill was Rs. 110, a 20% deduction would leave a remaining balance of 80% of 110, which is Rs. 88, not Rs. 180.
Option C: If the original bill was Rs. 130, the remaining 80% would be Rs. 104, which does not match the Rs. 180 stated in the problem.
Option D: If the original bill was Rs. 125, the remaining 80% would be Rs. 100. This is incorrect as the remaining amount is Rs. 180.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculating the original amount based on a percentage deduction and the remaining value as background academic context rather than a clinical decision trigger.
While not a clinical question, strong numeracy is a fundamental skill for nurses, essential for tasks like calculating medication dosages, IV drip rates, and interpreting lab results.
Percentage calculations are common in healthcare, for example, when assessing a patient's percentage weight loss/gain, calculating the body surface area affected by burns (Rule of Nines), or understanding statistical data in medical research.
What if the deduction was 30% instead of 20%? The remaining amount (Rs. 180) would then represent 70% of the original bill. The calculation would be 180 ÷ 0.70, resulting in an original bill of approximately Rs. 257.14.

How to Approach the Question

First, carefully read the question to identify the key information: a 20% deduction is made, and the remaining amount is Rs. 180.
Recognize that if 20% is deducted, the remaining portion represents 100% - 20% = 80% of the original total.
Translate this relationship into a mathematical equation. Let 'X' be the original bill. The equation is 0.80 × X = 180.
Solve for 'X' by isolating it. Divide the remaining amount by the remaining percentage (expressed as a decimal): X = 180 / 0.80.
Perform the calculation to find the value of X.
Compare your calculated result with the given options to find the correct answer.

Concept Tested & Keywords

Concept Tested: Calculating the original amount based on a percentage deduction and the remaining value.
Stem keywords: electricity bill, 20%, deducted, Rs. 180, original bill
Lead-in keywords: What is

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Practise the full RML 2023

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