Add using doubles minus one

Key notes:-

1. Introduction to Doubles:

  • Doubles are pairs of the same number added together.
    • Example: 4 + 4, 6 + 6, etc.

2. Understanding Doubles Minus One:

  • When we add using doubles minus one, we first think of the nearest double and then subtract one to find the answer.
  • Doubles minus one helps make addition quicker by connecting it to a known fact.
    • Example: To add 6 + 5, think of the nearest double, 6 + 6, which equals 12, and then subtract 1:
      • 6 + 5 = 12 – 1 = 11.

3. Steps for Doubles Minus One:

  • Identify the two numbers you are adding.
  • Find the nearest double (using the larger number).
  • Subtract 1 from the double to find the result.
    • Example: 7 + 6
      • Nearest double: 7 + 7 = 14
      • Subtract 1: 14 – 1 = 13
      • Therefore, 7 + 6 = 13.

4. Why Use Doubles Minus One:

  • This method helps students rely on their knowledge of doubles to make addition easier.
  • It reinforces mental math skills and makes number patterns more understandable.

5. Practice Examples:

  • 5 + 4 = 5 + 5 – 1 = 10 – 1 = 9
  • 8 + 7 = 8 + 8 – 1 = 16 – 1 = 15
  • 3 + 2 = 3 + 3 – 1 = 6 – 1 = 5

Learn with an example

🖌️Add the near doubles.
Hint: use the doubles fact 4+4=8.
4+3=

  • To add 4+3, you can use the strategy of doubles minus one. This is because 4 and 3 are near doubles.
  • Replace the 3 with 4–1 to make double 4s.
  • 4+3=4+4–1
  • Add the double 4s. Use the doubles fact 4+4=8.
  • 4+4–1=8–1
  • Subtract 1.
  • 8–1=7
  • So, 4+3=7.

🖌️Add the near doubles.
Hint: use the doubles fact 6+6=12.
6+5=

  • To add 6+5, you can use the strategy of doubles minus one. This is because 6 and 5 are near doubles.
  • Replace the 5 with 6–1 to make double 6s.
  • 6+5=6+6–1
  • Add the double 6s. Use the doubles fact 6+6=12.
  • 6+6–1=12–1
  • Subtract 1.
  • 12–1=11
  • So, 6+5=11.

🖌️Add the near doubles.
Hint: use the doubles fact 3+3=6.
3+2=

  • To add 3+2, you can use the strategy of doubles minus one. This is because 3 and 2 are near doubles.
  • Replace the 2 with 3–1 to make double 3s.
  • 3+2=3+3–1
  • Add the double 3s. Use the doubles fact 3+3=6.
  • 3+3–1=6–1
  • Subtract 1.
  • 6–1=5
  • So, 3+2=5.

Let’s practice!