Add multi-digit whole numbers

/
Use _ to understand multi-digit addition.
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Estimate to predict and check _
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Use strategies to mentally add multi-digit numbers.

1 answer

To effectively add multi-digit whole numbers, we can use a combination of strategies. Here's a breakdown of each method mentioned:

1. Understanding Multi-Digit Addition with Place Value

When you add multi-digit numbers, it's helpful to align them by their place values (ones, tens, hundreds, etc.). For example:

   245
 + 378
 ------

We can add from right to left, column by column.

2. Step-by-Step Addition

  1. Add the digits in the ones place: 5 + 8 = 13. Write 3 and carry over 1.
  2. Add the digits in the tens place plus the carry: 4 + 7 + 1 = 12. Write down 2 and carry over 1.
  3. Add the hundreds place plus the carry: 2 + 3 + 1 = 6.

So,

   245
 + 378
 ------
   623

3. Estimation

To estimate, round each number to the nearest ten or hundred and then add:

  • 245 rounds to 250
  • 378 rounds to 380

Estimating gives us:

   250
 + 380
 ------
   630

This helps us predict that the actual sum (623) is close to 630, indicating our addition is likely correct.

4. Mental Strategies

  • Break Apart: Break numbers into parts to make addition easier.

    • 245 can be seen as 240 + 5
    • 378 can be seen as 300 + 70 + 8
    • So, you can add: (240 + 300) + (70) + (5 + 8) = 540 + 70 + 13 = 623.
  • Compensation: If you add a little too much, you can adjust by subtracting that amount after.

    • For example, add 400 instead of 378:
    • 245 + 400 = 645, then subtract the 22 difference (400 - 378):
    • 645 - 22 = 623.

Summary

  • Use place value and carry when performing multi-digit addition.
  • Estimate what the answer should be to check your work.
  • Apply strategies like breaking apart numbers or using compensation to simplify mental calculations.

These methods can help you master multi-digit addition efficiently!

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