Decimal Dash Slides
Decimal Dash
Adding & Subtracting with Precision
5th Grade Math Standard Algorithm
Warm-up: Dollar Dash
Solve this problem mentally. Try to picture the numbers in your head.
$15.00 + $4.50
How did you line up the money?
Where is the decimal point?
LINE UP THE DECIMALS • PLACEHOLDER ZEROS • ADD/SUBTRACT
The Golden Rules
1
Line Up
Stack the numbers so the decimal points are in a straight vertical line.
2
Fill Gaps
Add placeholder zeros so every column has a digit to work with.
3
Calculate
Add or subtract from right to left. Don't forget to drop the decimal point!
Math with Mr. J
Watch closely. We will pause to practice together.
Pause Points: Get your pencils ready!
- • 0:26 - Write down all 4 problems
- • 2:45 - The "Invisible Decimal" mystery
- • 4:55 - The Subtraction Trap
Embedded media
Pause Point: 0:26
PAUSE VIDEO
Copy these four problems onto your paper. Leave space to solve!
Problem 1 (Addition) 45.6 + 3.89
Problem 2 (Whole Numbers) 15 + 4.88
Problem 3 (Subtraction) 35.6 - 9.67
Problem 4 (Sub. Whole Numbers) 23 - 8.8
Discussion Anchors
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Why does adding a zero at the end of a decimal not change the value, but adding it to a whole number does?
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How is 15 the same as 15.00? In what real-world context do we see this?
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What is the most common mistake students make with 23 - 8.8?
Graph Paper Master
One Box. One Digit. Perfect Alignment.
Activity Instructions:
- 1. Write the horizontal problem vertically on your grid.
- 2. Rule: Every digit, decimal, and symbol gets its own box.
- 3. Fill empty spaces with placeholder zeros.
- 4. Solve carefully!
Grid Master Worksheet
Grid Master Alignment
Decimal Addition & Subtraction
Name:
Date:
Mission: Perfect Alignment
Rewrite each horizontal problem vertically on the grid. Every digit, decimal point, and operation symbol must have its own box. Use placeholder zeros to fill any empty gaps before solving.
1 12.45 + 3.2
2 15 + 4.88
3 42.7 − 5.68
4 100 − 45.25
5 0.98 + 12.1
6 23 − 8.8
"Line up the decimals. Use placeholder zeros. Add or Subtract." — Mr. J
