Which two numbers should be interchanged to make the below equation mathematically correct?
16-4×5+3-2-15

Appeared in: DSSSB - 28 August 2019 (Shift-1)

Explanation

The correct answer requires interchanging the numbers 5 and 3.
The ambiguous expression 16-4×5+3-2-15 is interpreted as the equation 16 ÷ 4 × 5 + 3 - 2 = 15.
After swapping 5 and 3, the expression becomes 16 ÷ 4 × 3 + 5 - 2.
Following the BODMAS rule for the order of operations (Division, Multiplication, Addition, Subtraction), the calculation is: 4 × 3 + 5 - 2 = 12 + 5 - 2 = 15.
This result correctly matches the target value of 15.

Option A: Interchanging 4 and 3 results in the expression 16 ÷ 3 × 5 + 4 - 2. This calculation yields a non-integer result (approximately 28.67), which is not equal to 15.
Option B: Interchanging 5 and 2 results in the expression 16 ÷ 4 × 2 + 3 - 5. This evaluates to 4 × 2 + 3 - 5 = 8 + 3 - 5 = 6, which is not equal to 15.
Option C: Interchanging 4 and 2 results in the expression 16 ÷ 2 × 5 + 3 - 4. This evaluates to 8 × 5 + 3 - 4 = 40 + 3 - 4 = 39, which is not equal to 15.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mathematical Reasoning: Interchange of Numbers and Signs as background academic context rather than a clinical decision trigger.
Accurate mathematical calculation is a fundamental and non-negotiable skill in nursing to ensure patient safety during medication administration.
Errors in applying the correct order of operations (BODMAS) when calculating drug dosages can lead to significant medication errors, causing patient harm.
What if? If a nurse miscalculates an IV drip rate by making a simple arithmetic error, a patient could receive a medication too quickly (risking toxicity) or too slowly (rendering it ineffective).

How to Approach the Question

First, analyze the given string of numbers and operators. Since it's not a standard equation, infer the intended operators and the result (e.g., '16-4...' likely means '16 ÷ 4...' and the final number is the target result).
Establish the target equation to solve, which in this case is 16 ÷ 4 × 5 + 3 - 2 = 15.
Apply the BODMAS rule (Brackets, Orders, Division, Multiplication, Addition, Subtraction) for all calculations to ensure the correct order of operations.
Systematically test each option. For each pair of numbers, substitute them into the expression and calculate the new result.
Compare the result of each calculation with the target value (15). The option that yields the correct result is the answer.

Concept Tested & Keywords

QFj2J0RDvJ-yjOBD28h7Xq

Practise the full DSSSB - 28 August 2019 (Shift-1)

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