Rounding 5

Knowing how to round

Rounding:

  • Identify what increments are to be used (count by 10s, 100s, 1000s, ....)
  • Figure out which number your original number is closest to.

If the original number is half way between two numbers, you are not closest to the smaller number, so, we chose the larger number as the number that is closest ....

Examples:

  1. Rounding 45 to the nearest 10s.
    • Think of 30, 40, 50.
    • 45 is half way between 40 and 50.
    • Assume 45 is closer to 50.
    • The answer is 50.
  2. Rounding 450 to the nearest 100s.
    • Think of 300, 400, 500.
    • 450 is half way between 400 and 500.
    • Assume 450 is closer to 500.
    • The answer is 500.
  3. Round 340 to the closest 100.
    • Counting by 100, we have numbers like ... 100, 200, 300, 400.
    • 340 is closest to 300.
    • Our answer is 300.
  4. Round 5236 to the closest 10.
    • Counting by 10 (in the neighborhood of 5236).
    • we have numbers like ... 5200, 5210, 5220, 5230, 5240, 5250.
    • 5236 is closest to 5240.
    • Our answer is 5240.
  5. Round 15478 to the closest 1000.
    • Counting by 1000(in the neighborhood of 15478), we have numbers like ... 14000, 15000, 16000, 17000.
    • 15478 is closest to 15000.     (Why is 15478 closer to 15000 than to 16000?)
    • Our answer is 15000.
  6. Round 900 to the closest 10000.
    • Counting by 10000 (in the neighborhood of 900), we have numbers like ...  0, 10000, 20000.
    • 900 is closest to 0.
    • Our answer is 0.

Check Your Understanding

Test your skill at rounding....

  1. Give an example of when you might have a reason to round off a number. 
  2. When rounding the number 6720 to the nearest 1000, why would you think of the numbers 6000, 7000, and 8000? 
  3. When rounding 15 to the nearest 10, you would think of the numbers 0, 10, 20, 30.   Why would you chose the number 20 as the answer and not 10?