Lesson 4 — Activity 3: Adding and Subtracting Decimals
Completion requirements
Lesson 4 — Activity 3:
Adding and Subtracting
Decimals
When you have mastered how to add and subtract whole numbers, you are one very important step away from being able to add and subtract decimal numbers.
Important: When adding and subtracting decimal numbers, you must line up the decimal points one under the other.
When
this is done, the process of completing these operations is exactly the
same as it is when adding and subtracting whole numbers.
Follow these steps:
Step 1: Write the numbers that are to be added or subtracted one under the other. Be sure to line up the decimal points even though it doesn't look as though it is correct. (See first column below.)
Step 2: Fill
the “blank” spaces on the right with 0. This does not change the
value
of the number, but it will help to avoid the mistake of adding or
subtracting the wrong numbers. (See second
column
below.)
Step 3: Add or subtract the numbers in each
column, remembering to regroup and carry as needed.
Examples:
Addition
6.578 + 12.34 + 9.057 + 35.7 = ____
Numbers to Add |
Fill spaces with Zeros
|
6.578
|
6.578
|
63.675 |
Subtraction
7,852.387 – 596.46 = ____
Numbers to Subtract |
Fill spaces with Zeros
|
7,852.387
– 596.46
|
7,852.387
|
7,255.927 |
Let's try a real-life example!
Megan was paid $1,200 on October 1. Her rent is $450, which includes utilities, her phone bill this month is $35, and her cable bill is $65. She needs $125 for a bus pass. Whatever is leftover must be spent on groceries and emergencies that might arise during the month. If she budgets carefully, she should be able to go to the movies with her friends and maybe even go out to dinner once or twice!
$1,200 – $450 – $35 – $65 – $125 = $525
Megan has $525 left to buy groceries and perhaps spend a little on herself for movies and dinner. It is a tight budget!
Self-check!
Try this!
Answer these questions on your own first.
When you are finished, click on the tab below to check your answers!
Add the following decimals.
Be sure to line up your decimals first!
3.45 + 6.2 =
52.025 + 7.45 =
Subtract the following decimals.
Be sure to line up your decimals first!
6.86 – 3.4 =
89.682 – 5.45 =
