Adding Negative Numbers

1
Adding Negative Numbers

• -5 -2
• -7
• -10 -1 -3 -6

2
Using the Number Line
3
Using the Number Line

• Find (4) and (-4)
• Which is more? Which is Less?
• If this number represented dollars, which amount
  would you rather have?

4
Absolute Value

• Look at the numbers 3 and -3, marked with the
  blue dots
• How far are each of them from the zero?
• 3 places
• Absolute value is the value of the number without
  its sign.
• Each of these numbers has an Absolute Value of 3,
  even though their signs are different.

5
Where do we see negative numbers in our life?
6
Weather in Alaska
7
Using the number line to solve problems

• We count up for increases ( change)
• We count Down for decreases (- change)

8
Weather in Alaska
9
Using the number line to solve problems

• We count up for increases ( change)
• We count Down for decreases (- change)

10
Practice with Negative numbers

• 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

11
Practice with negative numbers

• EX 2 The low temperature for today was -2
  degrees. The high was 6 degrees. What was the
  total change in temperature today?
• (first find your starting place on your number
  line, and count up to 6. What is the difference
  between the two numbers?)
• Answer 8
• Equation -2 8 6

12
Practice with negative numbers

• 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 Tommys 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

13
Rules for Adding Negative numbers

• 1 When both numbers are positive, you simply add
  them together.
• 8 3 11
• 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.
• (-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.
• (-4) (-5) -9