Decimal Line Up Challenge

Christina Bellucci

Tier 1

Worksheet

Decimal Addition Challenge: Line 'Em Up!

Instructions: For each problem, carefully line up the decimal points and then add. Show your work!

5.23 + 12.8
0.75 + 1.254
8.006 + 3.92
17.02 + 3.9
2.678 + 9.3
6.7 + 0.385
11.23 + 4.9
0.98 + 12.005

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Lesson Plan

Decimal Line Up Challenge

Students will accurately add decimals by demonstrating correct alignment of place values, improving their precision and understanding of decimal operations.

Mastering decimal addition with proper alignment is crucial for real-world applications like managing money, measuring ingredients, and understanding data. This lesson strengthens foundational math skills and attention to detail.

Audience

7th Grade Students

Time

30 minutes

Approach

Students will work independently on a worksheet, focusing on self-correction and accurate alignment.

Materials

Decimal Addition Challenge Worksheet, - Decimal Addition Slide Deck, and - Decimal Addition Answer Key

Prep

Review Materials

5 minutes

Review the Decimal Addition Challenge Worksheet and Decimal Addition Answer Key to familiarize yourself with the problems.
- Ensure the projector/screen is set up for the Decimal Addition Slide Deck.

Step 1

Introduction & Warm-Up

5 minutes

Display the first slide of the Decimal Addition Slide Deck with a warm-up question.
- Briefly review the importance of lining up decimal points when adding, without giving away solutions to the worksheet problems.

Step 2

Worksheet Distribution & Independent Work

20 minutes

Distribute the Decimal Addition Challenge Worksheet.
- Explain to students that the problems are intentionally not lined up and their first step is to correctly align them.
- Circulate around the room to provide individual support and clarification as students work independently.

Step 3

Wrap-Up & Cool-Down

5 minutes

Bring the class back together.
- Display the cool-down slide from the Decimal Addition Slide Deck.
- Collect the Decimal Addition Challenge Worksheet for review using the Decimal Addition Answer Key.
- Briefly discuss one common mistake observed or a helpful strategy.

Slide Deck

Warm-Up: Think Fast!

What is 3.5 + 2.15?

Take a moment to solve this in your head or on scratch paper. We'll share answers in a moment!

Welcome students and prepare them for a quick warm-up. This question is designed to activate prior knowledge on decimals and addition in general, without specifically focusing on alignment yet.

Why Line Up Decimals?

When adding decimals, it's super important to line up the decimal points!

This ensures you're adding tenths to tenths, hundredths to hundredths, and so on.
Think of it like adding whole numbers: you line up the ones, tens, hundreds... decimals work the same way!
If numbers have different lengths, you can add zeros as placeholders without changing their value (e.g., 5.23 is the same as 5.230).

Briefly review the concept of place value and why aligning decimal points is critical. Emphasize that misaligned decimals lead to incorrect answers. This is a quick reminder before they tackle the worksheet.

Your Challenge: Line 'Em Up!

Today's worksheet has decimal addition problems where the numbers are not lined up for you.

Your mission:

Carefully write out each problem, making sure to align the decimal points.
Add the numbers.
Show your work!

Take your time and pay attention to detail. Good luck!

Introduce the worksheet and explain the task. Reiterate that the problems are not lined up and that is part of the challenge. Encourage careful work.

Cool-Down: Decimal Detective

What was the trickiest part about lining up decimals today?

What is one strategy you used to make sure your decimals were aligned correctly?

Conclude the lesson by having students reflect on their learning. This helps solidify the main objective. Collect worksheets after this.

Answer Key

Decimal Addition Challenge: Answer Key

Here are the solutions with the correct alignment and steps shown.

5.23 + 12.8
```
  5.23
+12.80
-------
 18.03
```
0.75 + 1.254
```
  0.750
+ 1.254
-------
  2.004
```
8.006 + 3.92
```
  8.006
+ 3.920
-------
 11.926
```
15.1 + 0.08 + 7.35
```
 15.10
  0.08
+  7.35
-------
 22.53
```
2.678 + 9.3
```
  2.678
+ 9.300
-------
 11.978
```

4.1 + 1.009 + 0.52

  4.100
  1.009
+ 0.520
-------
  5.629

10.05 + 2.3 + 0.875

 10.050
  2.300
+ 0.875
-------
 13.225

0.003 + 1.5 + 8.24

  0.003
  1.500
+ 8.240
-------
  9.743