Add using doubles minus one

Key notes:-

🔢 What are doubles?

Doubles are when both numbers are the same.

  • Example: 4 + 4 = 8 😊
  • Example: 6 + 6 = 12 🎉

➖➕ What is “doubles minus one”?

When the numbers are next to each other (like 5 and 6), we use the bigger number’s double and subtract one.

Example: 5 + 6 is close to 6 + 6

  • 6 + 6 = 12
  • 12 − 1 = 11 ✔️

🧠 Why use doubles minus one?

It helps students add faster using facts they already know.

  • It is easier to remember doubles! 🤩
  • Then subtract 1 to get the answer.

✏️ Examples

  • 4 + 5 → Use 5 + 5 = 10 → 10 − 1 = 9 🌟
  • 7 + 6 → Use 7 + 7 = 14 → 14 − 1 = 13 🌼
  • 9 + 8 → Use 9 + 9 = 18 → 18 − 1 = 17 🌈

💡 When do we use doubles minus one?

Use this strategy when the numbers are consecutive (next to each other).

  • 2 and 3
  • 3 and 4
  • 8 and 9
    These pairs work well! 🙌

🧩 Visual Tip

If you see two numbers like N and N+1,
📌 Think: (N+1) + (N+1) − 1
This makes addition faster and more fun! ✨

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!