Adding Integers and Developing Rules

-9 + -6

• Correct answer is -15• What are you doing with the

numbers?• If both signs are negative how does

that affect your answer?

10 + -6

• Correct answer is 4• What are you doing

with the numbers?• If the signs are

different, how does that affect your answer?

-12 + 7

• Correct answer is -5

• What are you doing with the numbers?

• If the signs are different, how does that affect your answer?

Develop Rules

• If you are adding integers with the same sign, what do you do? (Example 1)– Add the absolute value of the numbers & keep

the sign

• If you are adding integers with different signs, what do you do? (Example 2 and 3)– Subtract the absolute value of the numbers, and

keep the sign of the greater absolute value.• Absolute value – how far the number is away from zero

Example 1-9 + -3

Adding integers with the same sign

Add the numbers

Keep the sign

9 + 3 = 12

-12

-9 + -3 = -12

Example 2-15 + 7

Adding integers with different signs

Subtract the numbers

Take the sign of the greater absolute value.

15 – 7 = 8

-15 has the greater absolute value.

-15 + 7 = -8

Example 29 + -4

Adding integers with different signs

Subtract the numbers

Take the sign of the greater absolute value.

9 – 4 = 5

9 has the greater absolute value.

9 + -4 = 5

Practice Problems1. -18 + -4 =

2. 25 + -10 =

3. -13 + -5 =

4. -19 + 6=

5. -14 + 14=

6. -6 + -3 + 7

7. -5 + 8 + -6

-22

15

-18

-13

0

-9 + 7 = -2

3 + -6 = -3

Word Problems with Integers1. At 8am the temperature was -6°F. At noon, the

temperature rose 9 degrees. What was the temperature at noon?

-6 + 9 = 3°F The temperature at noon was 3°F.

2. A submarine is situated 400 feet below sea level. If it rises 125 feet, what is its new position?

-400 + 125 = -275The new position of the submarine is 275 feet below sea

level.