Download 10-2 Adding Integers

10-2 Adding Integers
What You’ll Learn:
•To add integers with the same sign
•To add integers with different signs
Why?
•To find the results of a Frog-Jumping Contest
Using a Number Line
You start at 0, facing
the positive direction.
You move forward for a
positive integer or backward
for a negative integer.
Here is how to find 3 + 2
Start at 0. Face the
positive direction. Move
forward 3 units for 3.
Then move forward 2 more
units for 2. You stop at 5.
Find -3 + (-2)
Start at 0. Face the positive
direction. Move backwards
3 units for -3.
I wonder
Oh that’s
right,why
they are
there
arethat
parentheses?
to
show
a negative
number is being added.
Then move backward
2 more units for -2.
You stop at -5.
Find each sum
-1 + (-3)
-4
2 + 10
12
(-5) + (-4)
-9
The sum of two negative integers is _____?
NEGATIVE
Adding Integers with the Same Sign
When adding integers with the same sign, add and keep
the sign.
9 + 18
-3 + (-7)
9 + 18 = 27
-3 + (-7) = -10
The sum of two
positive integers is
positive.
The sum of two
negative integers is
negative.
Find each sum
7+9=
16
-9 + (-12) =
-21
-6 + (-10) =
-16
12 + 23 =
35
You can also use a number line to model the addition of
integers with different signs. Here is how to find 3 + (-2)
Start at 0, and face the
positive direction. Move
forward 3 units for 3.
Then move backward
2 units for -2. You
stop at 1.
Find each sum.
4 + (-1) =
3
-1 + 4 =
3
3 + (-2)
1
Adding Integers with Different Signs
To add integers with different signs, subtract the two numbers
and keep the sign of the larger number.
8 + (-5) =
8-5=3
8 is the larger
number so the sign
is positive
8 + (-5) = 3
-9 + 6
9-6=3
The 9 is larger so the
answer is negative.
-9 + 6 = -3
Find each sum
7 + (-10) =
-3
-11 + 4 =
-7
12 + (-3) =
9
Suppose you enter your frog in a jumping contest. The judge
records each jump. A jump toward the finish line is a
positive number. A jump away from the finish line is a
negative number.
Your frog jumps 4 feet toward the finish line. Then he
jumps 6 feet away. What is the result of these jumps?
4 + (-6) = -2 feet