1. Frigid Fridays
On each Friday last January, the temperature was a record low temperature for the date. On Friday, January 30, the mercury dropped to 5°F, which was 7 degrees higher than the low temperature on the Friday before. The low on January 9 was 2 degrees lower than the low temperature on January 16. On the first Friday of the month, the low temperature was 3 degrees lower than that on January 23. The low temperature on the Friday in the middle of the month was 6 degrees higher than the low temperature on the first Friday. The temperature on the first Friday, January 2nd was -5°F.
What was the low temperature reading for each Friday of the month?

2. Solution Date Low Temperature Reading January 2 -5°F January 9 -1°F

3. Subtracting Integers
Lesson 3-5

4. First let’s review adding integers!
When the signs are the same, add the integers and keep the sign.
When the signs are different, subtract the integers and keep the sign of the larger digit.

5. Add Integers 13 18 + (-5) = -25 -10 + (-15) = 16 6 + 10 = -5
-38
18 + (-5) =
-10 + (-15) = = =
-18 + (-20) =

6. Rule for subtracting integers
To subtract integers, add the opposite.
What does this mean?
Keep, Change, Change
Keep the 1st integer the same
Change the subtraction sign to addition.
Change the sign of the second integer.
Then follow the rules for addition.

7. Let’s try an example.
-5 – (-2)
keep, change, change
Opposite sign subtract and keep the sign of the larger digit.
= -3

8. Let’s try an example -4 – 3 -4 + (-3) keep, change, change
Same sign add the integers and keep the sign.
-4 + (-3) = -7

9. Example 6 – (-4) Keep, Change, Change 6 + 4 10
Now follow the rules for adding integers!

10. Example -5 – 8 Keep, Change, Change -5 + -8 -13
Now follow the rules for adding integers!

11. Example 18 - 20 Keep, Change, Change 18 + -20 -2
Now follow the rules for adding integers!

12. Time for some practice! -14 -9 – 5 = 27 – (-8) = -3 – (-1) = 35
-8 – 9 =
14 – 17 =
4 – (-19) = 35 -2
-17 -3 23

13. One more time what is the rule?
Add the opposite.
Keep, Change, Change
Keep the 1st integer, Change the sign to addition, Change the 2nd integer.
Then follow the rules for adding integers.

14. Don't Forget
Homework:
Lesson 3-5 # 2-24 evens