Question

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

Answer 1

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!