Lecture: Adding and Subtracting Decimals with Mr. J

Introduction

• Focus on adding and subtracting decimals.
• Steps to successfully perform these operations.
• Four example problems: two addition and two subtraction.

Key Steps

1. Set Up the Problem

   • Rewrite the problem vertically (up and down).
   • Align the decimals.

2. Use Placeholder Zeros

   • Insert placeholder zeros to align decimal places.
   • Only applicable to decimals, not whole numbers.

3. Add or Subtract

   • Perform operation on aligned numbers.
   • Bring decimal straight down into the answer.

Example Problems

Addition

• Problem 1: 45.6 + 3.89

  • Rewrite as:
    • 45.60
    • • 3.89
  • Add:
    • 0 + 9 = 9
    • 6 + 8 = 14 (carry 1)
    • 1 + 5 = 6 + 3 = 9
    • Result: 49.49

• Problem 2: 15 + 4.88

  • Rewrite as:
    • 15.00
    • • 4.88
  • Add:
    • 0 + 8 = 8
    • 0 + 8 = 8
    • 5 + 4 = 9
    • Result: 19.88

Subtraction

• Problem 3: Subtract involving borrowing

  • Example: (not specified exact numbers)
  • Align decimals and subtract using borrowing.
  • Result: 25.93

• Problem 4: 23 - 8.8

  • Rewrite as:
    • 23.0
    • • 8.8
  • Subtract using borrowing:
    • 0 - 8 (borrow needed)
    • Result: 14.2

Summary

• Important to line up decimals correctly.
• Use placeholder zeros to facilitate easier addition or subtraction.
• Bring the decimal straight down into the result.

Conclusion

• Practice these steps to become proficient.
• Thank you for watching.