Adding a positive number to a negative number

Aviation Mechanic General (AMG) practice question 24 of 25 on Mathematics. ACS element AM.I.H.R2 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONAn account is in debt by $100, represented as −100. If $45 is added to the account, what is the result of −100 + 45?

A−55
B−145
C55

Show the answer and explanation

Correct answer: A. −55

A — correct Adding 45 to a debt of 100 leaves a debt of 55: −100 + 45 = −55.
B — incorrect −145 would result from adding two negative numbers (−100 + −45); here 45 is positive.
C — incorrect The debt is larger than the amount added, so the result remains negative.

BACKGROUND

The sum of two positive numbers is positive, and the sum of two negative numbers is negative. The sum of a positive and a negative number can be positive or negative, depending on the values of the numbers. The handbook suggests thinking of a negative number as debt: if you are in debt by $100 (−100) and add $45 to the account, you are now only $55 in debt (−55), so −100 + 45 = −55. The same rule applies to weight and balance, where weight removed carries a minus sign and weight added carries a plus sign.

STUDY TIP

When signs differ, subtract the smaller absolute value from the larger and keep the sign of the larger.

KEY POINTS

Positive + negative: sign depends on which value is larger.
−100 + 45 = −55.
Weight removed from an aircraft is treated as negative.

SOURCES

FAA-H-8083-30B ch03 "Addition of Positive & Negative Numbers"

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