Positive numbers are numbers that are greater than zero. Negative numbers are numbers less than zero. [Figure 1-8] Signed numbers are also called integers.

#### Addition of Positive and Negative Numbers

The sum (addition) of two positive numbers is positive. The sum (addition) 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. A good way to visualize a negative number is to think in terms of debt. If you are in debt by $100 (or, −100) and you add $45 to your account, you are now only $55 in debt (or −55).

Therefore: −100 + 45 = −55.

Example: The weight of an aircraft is 2,000 pounds. A radio rack weighing 3 pounds and a transceiver weighing 10 pounds are removed from the aircraft. What is the new weight? For weight and balance purposes, all weight removed from an aircraft is given a minus sign, and all weight added is given a plus sign.

2,000 + −3 + −10 = 2,000 + −13 = 1987

Therefore, the new weight is 1,987 pounds.

#### Subtraction of Positive and Negative Numbers

To subtract positive and negative numbers, first change the “–” (subtraction symbol) to a “+” (addition symbol), and change the sign of the second number to its opposite (that is, change a positive number to a negative number or vice versa). Finally, add the two numbers together.

Example: The daytime temperature in the city of Denver was 6° below zero (−6°). An airplane is cruising at 15,000 feet above Denver. The temperature at 15,000 feet is 20° colder than in the city of Denver. What is the temperature at 15,000 feet?

Subtract 20 from −6: −6 – 20 = −6 + −20 = −26

The temperature is −26°, or 26° below zero at 15,000 feet above the city.

#### Multiplication of Positive and Negative Numbers

The product of two positive numbers is always positive. The product of two negative numbers is always positive. The product of a positive and a negative number is always negative.

#### Division of Positive and Negative Numbers

The quotient of two positive numbers is always positive. The quotient of two negative numbers is always positive. The quotient of a positive and negative number is always negative.

Examples: