# Summing It Up

## How do you sum it up?

## OBJECTIVE: To learn how to add integers

In this lesson, you'll learn how to add INTEGERS.
There are two cases:
Case 1—two INTEGERS having the SAME signs
Step 1. ADD their ABSOLUTE values.
Step 2. Apply the COMMON sign of the ADDENDS to the SUM.
Examples: 6 + 7 = 13
(-6) + (-7) = -13
Case 2—two INTEGERS having DIFFERENT signs
Step 1. SUBTRACT their ABSOLUTE values.
Step 2. Apply the sign of the NUMBER having the GREATER absolute value to the SUM.
Examples: 6 + (-7) = -1
(-6) + 7 = 1
NOTE:
1. If one of the integers is ZERO, the sum is the other integer since ZERO is the IDENTITY element for ADDITION.
2. The plus sign ( + ) is often omitted in the sum.

The NUMBER LINE can be used to demonstrate how to add INTEGERS.
Use the applet below for practice.
Instructions:
1. Position the WHITE DOT of the BOTTOM arrow at the ORIGIN ( 0 ).
2. Drag the WHITE DOT of the TOP arrow to coincide with the arrowhead of the BOTTOM arrow.
3. The NUMBER (or COORDINATE) under the arrowhead of the TOP arrow is the ANSWER.
Repeat as many times as necessary to master the concept.

## TRY IT!

## NOW LET'S TAKE AWAY THE NUMBER LINE!

## In this lesson, you learned how to add integers.

In future lessons, you'll learn how to perform other operations on integers. Did you have FUN today!

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