Choose numbers with a particular sum or difference

Key notes :

🧨1. Understanding the Concept

  • Sum: The result of adding two or more numbers together.
    • Example: The sum of 8 and 7 is 8+7=15
  • Difference: The result of subtracting one number from another.
    • Example: The difference between 12 and 5 is 12−5=7

🎉2. Identifying the Task

  • Choosing Numbers: The goal is to select pairs or sets of numbers that, when added or subtracted, result in a specified sum or difference.
    • Example (Sum): Choose two numbers that add up to 20. (Possible pairs: 12 and 8, 15 and 5, etc.)
    • Example (Difference): Choose two numbers where the difference is 6. (Possible pairs: 14 and 8, 20 and 14, etc.)

🎊3. Strategies for Finding the Right Numbers

  1. Addition Strategy:
    • Start with the Desired Sum: Determine the target sum.
      • Example: For a sum of 18, think of pairs like 10+8 or 12+6
    • Use Known Facts: Recall basic addition facts to find pairs quickly.
      • Example: For a sum of 15, use 7+8 or 10+5.
  2. Subtraction Strategy:
    • Start with the Larger Number: Begin with a number and subtract smaller numbers to find the correct difference.
      • Example: For a difference of 7, use 14−7 or 20−13
    • Consider Multiple Options: There are often several correct answers, especially if using larger numbers.
      • Example: For a difference of 9, you could use 18−9, 20−11, or 30−21.
  3. Using Number Bonds:
    • Number Bonds: Understanding pairs of numbers that add up to a certain number helps in quickly identifying sums.
      • Example: Number bonds for 10 include 1+9, 2+8, 3+7 etc.
    • Apply to Larger Sums: Extend this concept to larger numbers by adjusting the tens and units.
      • Example: For a sum of 25, consider 20+5, 18+7, or 15+10.
  4. Visualization with Number Lines:
    • Addition on a Number Line: Start at one number and move right to reach the sum.
    • Subtraction on a Number Line: Start at the larger number and move left to find the difference.
  5. Using Mental Math:
    • Estimate and Adjust: Start with numbers close to what you think might work, then adjust by adding or subtracting.
      • Example: For a sum of 30, try 20+10and adjust if needed.

🎇4. Practice with Examples

  • Sum Examples:
    • Choose two numbers with a sum of 50.
      • Possible Answers: 25+25, 30+20, 40+10.
    • Choose three numbers with a sum of 60.
      • Possible Answers: 20+20+20, 30+15+15, 25+25+10
  • Difference Examples:
    • Choose two numbers with a difference of 9.
      • Possible Answers: 18−9, 20−11, 25−16.
    • Choose two numbers with a difference of 15.
      • Possible Answers: 30−15, 40−25, 20−5.

Learn with an example

🗼 Choose two numbers from the box to complete the subtraction number sentence .

64 331 366 699

____ – _____ = 35

  • Look for numbers in the box that are greater than 35.
  • Try 64. What number can you subtract from 64 to get 35?
  • 64 − 29 = 35
    29 is not in the box.
  • Try 331. What number can you subtract from 331 to get 35?
  • 331 − 296 = 35
    296 is not in the box.
  • Try 366. What number can you subtract from 366 to get 35?
  • 366 − 331 = 35
    331 is in the box.
  • The subtraction number sentence is 366 − 331 = 35.

🗼 Choose two numbers from the box to complete the sentence .

3 42 59 68

___ and ___ have a sum of 71 .

  • Try 3. What number can you add to 3 to get 71?
  • 3 + 68 = 71
    68 is in the box.
  • The numbers 3 and 68 have a sum of 71.

🗼 Choose two numbers from the box to complete the addition number sentence.

2 5 89 306

___ + ____ = 308

  • Try 2. What number can you add to 2 to get 308?
  • 2 + 306 = 308
  • 306 is in the box.
  • The addition number sentence is 2 + 306 = 308.

Let’s practice!