Rule 2: To add two numbers with unlike signs (i.e., one is positive and one
is negative), subtract the absolute values of the numbers and give the
answer the sign of the number with the larger absolute value.EXAMPLE
Add (þ5)þð 2 Þ:SOLUTION
Since the numbers have different signs, subtract the absolute values of the
numbers, 5 2 ¼3. Then give the 3 a positive sign since 5 is larger than 3 and
the sign of the 5 is positive. Therefore, (þ5)þð 2 Þ¼þ3.EXAMPLE
Add (þ3)þð 4 Þ:SOLUTION
Since the numbers have different signs, subtract the absolute values of the
numbers, 4 3 ¼1. Then give the 1 a negative sign since 4 is larger than 3.
Therefore, (þ3)þð 4 Þ¼1. This rule can be demonstrated by looking at
the number lines shown in Fig. 2-4.In the first case, start at 0 and move five units to the right, ending onþ5.
From there, move 2 units to the left. You will end up atþ3. Therefore, (þ5)
þð 2 Þ¼þ3.
In the second case, start at 0 and move 3 units to the right, ending atþ3.
From there, move 4 units to the left. You will end on1. Therefore, (þ3)þ
(4)¼1.
To add three or more integers, you can add two at a time from left to right.22 CHAPTER 2 Integers
Fig. 2-4.