Why is subtracting a negative the same as adding a positive?

Removing a debt increases value: subtracting −5 is equivalent to adding +5. Therefore 12 − (−5) = 17.

What’s the fastest way to add two negative numbers?

Add their absolute values, then add a negative sign: (−14) + (−6) = −20.

How do I avoid mixing up rules under pressure?

Use the mantra: “minus a minus is a plus.” Convert every subtraction of a negative into addition.

Where will I use this in a real case interview?

Net profit/loss, budget variances, and trend analysis (e.g., −$2M savings) rely on accurate handling of negatives.

Negative Number Tricks: Case Interview Math Guide

Negative Number Tricks

How do you add and subtract negative numbers in mental math? Adding a negative is like subtracting a positive. Subtracting a negative is like adding a positive. These tricks are essential for analyzing profit/loss, budget deficits, or declining KPIs in case interviews.

Why Negative Numbers Matter in Consulting

You’ll constantly encounter negatives: quarterly losses, cost overruns, declining market share, or negative growth rates.

Calculate net profit/loss across business units
Analyze budget variances (actual vs forecast)
Assess performance trends (e.g., “revenue declined by −$2M QoQ”)
Avoid embarrassing calculation errors under pressure

Adding Negative Numbers

Core rule: adding a negative is the same as subtracting its positive value.

a

Adding a Negative to a Positive

Subtract the absolute value of the negative number from the positive number.

Example: 15 + (−7) = 15 − 7 = 8

b

Adding Two Negatives

Add the absolute values and keep the negative sign.

Example: (−6) + (−9) = −(6 + 9) = −15

Subtracting Negative Numbers

Core rule: subtracting a negative is the same as adding a positive.

a

Subtracting a Negative from a Positive

Add the absolute value of the negative number to the positive number.

Example: 12 − (−5) = 12 + 5 = 17

b

Subtracting a Negative from a Negative

Convert the subtraction to addition, then apply the rules for adding negatives.

Example: (−8) − (−3) = (−8) + 3 = −5

Real‑World Consulting Applications

Performance Change — Q1 = −$3M, Q2 = −$1M → change = (−1) − (−3) = −1 + 3 = +$2M improvement

Stock Value Trend — (−5) + (−3) = −$8

Ready to Drill This Skill?

Reading is not enough. To make negative number operations automatic under pressure, you need timed, focused practice.

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Practice Negative Numbers in Fast Math

Our Fast Math drills generate unlimited problems with negatives, provide instant feedback, and track your speed. Start with untimed mode, then ramp up to interview conditions.

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Apply It in Real Business Scenarios

Try our Business Math exercises where you'll use negative numbers to analyze profit/loss, budget variances, and performance trends.

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