Adding & Subtracting Decimals Notes
What is the answer to an addition problem? __________________
What is the answer to a subtraction problem? ____________
Example 1: Megan solved the problem 15 + 7 and got a sum of 85. Jack
solved the same problem and got a sum 15 + 7 = 22. Who is correct? How do
you know?
It might help to see their work:
Megan:
15
+ 7
85
1
Jack: 1 5
+ 7
22
Example 2: Tommy solved the problem 33.7 + 2.55 and got a sum of 5.92.
Anna solved the same problem and got 33.7 + 2.55 and got a sum of 36.25.
Who is correct? How do you know?
Here is their work:
1
Tommy: 33.7
+ 2.55
5.92
1
Anna: 33.70
+ 2.55
36.25
WHAT DO YOU NEED TO DO WHEN SETTING UP A
ADDITION OR SUBTRACTION PROBLEMS WITH DECIMALS?
WHY? ___________________________________________
Other Situations:
Adding or subtracting a WHOLE NUMBER and a DECIMAL.
1. If you do not see a decimal then you add the decimal to
the end of the number.
Example: The number 7 is really 7.0 or 7.00 or 7.000
The number 154 is really 154.0 or 154.00
The number 66 is really ________________
The number 12443 is really ______________
2. After you line up the decimal points, you must ANNEX
zeros (fill the empty spaces to the right of the decimal.)
Example: 6 – 2.3
6 .0
- 2. 3
* When solving – Bring the decimal point straight down
Your turn to practice:
4.78 + 12.5
234 – 25.5
2.649 + .75 + 1.784