Negative numbers!
Adding negatives
• -3 + 5 = 2
• -6 + 3 = -3
• -7 + 7 = 0
• -10 + 16 = 6
• -3.5 + 0.5 = -3
-15 -14 -13 -12 -11 -10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Adding negatives
• 5 + -3 = 2
• 2 + -7 = -5
• -4 + -1 = -5
• -10 + -10 = -20
• -6.2 + -0.2 = -6.4
-15 -14 -13 -12 -11 -10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
What happens when you subtract a negative number?
Add an ice cube to a drink of 5oC.
What is the new temperature?
5 + -1 = 4
What is the temperature if we take the ice cube out?
4 - -1 = 5
Subtracting a negative number has an increasing effect.
What happens when you subtract a negative number?
Add 2 ice cubes to a drink of 4oC.
What is the new temperature?
4 + -2 = 2
What is the temperature if we take the ice cubes out?
2 - -2 = 4
Subtracting a negative number has an increasing effect.
Judging the contest!
4 people are judging a competition.
These are the scores they give.
-4
3
-2
5
What is the total score? -4 + 3 + -2 + 5 = 2
What if there were only 3 judges?
2 - -2 = 4
Subtracting a negative number has an increasing effect.
Subtracting negatives
• 4 - -3 =
7
• -6 - -3 = -3
• -6 - -8 = 2
• 12 - -5 = 17
• -9 - -12 = 3
-15 -14 -13 -12 -11 -10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15