Transcript Adding Negative Numbers - The John Crosland School

Adding Negative Numbers
-5
-2
-7
-10
-1
-3
-6
Using the Number Line
Using the Number Line
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Find (+4) and (-4)
Which is more? Which is Less?
If this number represented dollars, which
amount would you rather have?
Absolute Value
Look at the numbers +3 and -3, marked with the blue dots
How far are each of them from the zero?
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3 places
Absolute value is the value of the number without it’s sign.
Each of these numbers has an Absolute Value of 3, even though
their signs are different.
Where do we see negative
numbers in our life?
Weather in Alaska
Temperuture (degrees)
Average Tempuratures for Alaska
80
60
40
High
Low
20
0
-20
J
F
M
A
M
J
J
Month
A
S
O
N
D
Using the number line to solve
problems
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We count up for
increases (+ change)
We count Down for
decreases (- change)
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
Weather in Alaska
Temperuture (degrees)
Average Tempuratures for Alaska
80
60
40
High
Low
20
0
-20
J
F
M A M
J
J
Month
A
S O
N D
Using the number line to solve
problems


We count up for
increases (+ change)
We count Down for
decreases (- change)
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
Practice with Negative numbers
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EX 1:
Last year on Christmas
Day, it was -10 degrees.
This year will be 10
degrees warmer. What
temperature will it be on
Christmas Day this year?
(First: find your starting
point on you number line.
Then, decide what
“warmer” means. Will
you be counting up or
down?)
Answer: 0 degrees
Equation: -10 + 10 = 0
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
Practice with negative numbers
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EX 2: The low temperature
for today was -2 degrees.
The high was 6 degrees.
What was the total change
in temperature today?
10
9
8
7
6
5
4
(first: find your starting
place on your number line,
and count up to 6. What is
the difference between the
two numbers?)
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Answer: 8
Equation: -2 + 8 = 6
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
Practice with negative numbers
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EX 3: Tommy and his family are
planning a trip to Maine for
Christmas. The average
temperatures in December are
-10 degrees! Thankfully, this
year has been a lot warmer so
far, and the weatherman said
he expects it to be 15 degrees
warmer this year.
What temperature can Tommy’s
family expect to have?
(hint: find your starting point
on your number line, and count
“up” 15 degrees.)
Answer: 5 degrees
Equation: -10 + 15 = 5
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
Rules for Adding Negative
numbers:
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1: When both numbers are positive, you simply add them
together.
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2: When one number is negative and one number is
positive: pretend both numbers are positive, subtract the
smaller number from the larger number, and then give
your answer the sign of the number that would be larger
if they were both positive.
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8 + 3 = 11
(-7) + 3 = -4
3: When both numbers are negative: Add the two
numbers together as you would if they were both
positive; then put the negative sign in front of the
answer.
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(-4) + (-5) = -9