Which two signs should be interchanged to make the below equation mathematically correct?
7 * 3 + 12 / 2 - 4 = 23

Appeared in: DSSSB - 29 August 2019 (Shift-1)

Explanation

The given equation is already mathematically correct as written.
The order of operations (BODMAS/PEMDAS) dictates that multiplication and division are performed before addition and subtraction.
Step 1 (Multiplication/Division): 7 * 3 becomes 21, and 12 / 2 becomes 6.
Step 2 (Addition/Subtraction): The expression simplifies to 21 + 6 - 4.
Step 3 (Final Calculation): 27 - 4 equals 23, which confirms the equation is true.

Option A: Interchanging the '+' and '-' signs results in the equation 7 * 3 - 12 / 2 + 4. Following BODMAS, this calculates to 21 - 6 + 4, which equals 19, not 23.
Option B: Interchanging the '×' and '+' signs results in the equation 7 + 3 * 12 / 2 - 4. Following BODMAS, this calculates to 7 + 18 - 4, which equals 21, not 23.
Option C: Interchanging the '-' and '×' signs results in the equation 7 - 3 + 12 / 2 * 4. Following BODMAS, this calculates to 7 - 3 + 24, which equals 28, not 23.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Order of mathematical operations (BODMAS/PEMDAS) as background academic context rather than a clinical decision trigger.
Accurate application of the order of operations is a critical safety skill in nursing, especially for medication dosage calculations.
Errors in calculation can lead to significant underdosing or overdosing, posing a direct risk to patient safety.
What if? If a nurse miscalculates a multi-step infusion rate by performing addition before division, it could lead to the medication being delivered too slowly (sub-therapeutic) or too quickly (toxic).

How to Approach the Question

First, identify that the question is a mathematical reasoning problem that requires applying the order of operations (BODMAS/PEMDAS).
Always start by evaluating the equation exactly as it is given.
Follow the BODMAS/PEMDAS sequence: Brackets, Orders, Division/Multiplication (left-to-right), Addition/Subtraction (left-to-right).
Calculate 7 * 3 = 21 and 12 / 2 = 6 first.
Then, calculate 21 + 6 - 4 = 23.
Since the result matches the equation, conclude that no changes are needed and select the corresponding option.

Concept Tested & Keywords

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Practise the full DSSSB - 29 August 2019 (Shift-1)

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