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### Course: 3rd grade > Unit 3

Lesson 9: Addition and subtraction word problems# Addition, subtraction, and estimation: FAQ

Frequently asked questions about addition, subtraction, and estimation.

**Why is it important to learn how to round?**

Rounding numbers is helpful when we want to estimate sums or differences. For example, if we want to add $235$ and $286$ , we might round both numbers to the nearest hundred and estimate that the sum is around $500$ .

**What are some strategies for adding or subtracting two or three-digit numbers?**

There are many ways we can add numbers together. One way is to break one of the numbers down and add or subtract each part separately. Another strategy is to use groups of $10$ or $100$ or by using a number line.

**What does it mean to "regroup" when adding numbers?**

When we regroup, we carry over numbers from one place value to another. For example, when we add $38$ and $47$ , we end up with $15$ in the ones place. But we can't write $715$ as the sum because we only use one digit in the ones place. So we regroup by carrying over the $10$ from the $15$ into the tens place, which gives us a sum of $85$ .

**Why is it important to learn these skills?**

We use addition, subtraction, and estimation in our everyday lives all the time! For example, when we go to the store, we might estimate how much our items will cost before we get to the checkout line. Or when we're baking, we might need to add or subtract measurements to get the right amount of ingredients.

## Want to join the conversation?

- some times the word problem dose not make sens, so then it is hard to solve.(could you help?)(6 votes)
- i agree with this(4 votes)
- How many is the unit test?(5 votes)
- there i 12 unit tests!(2 votes)

- Why does the unit test have so much question.(4 votes)
- that's what I'm saying(3 votes)

- when will our class learn negative numbers?(5 votes)
- why does unit three not have adding 4 digit numbers its a part third grade math mcas tcap and other national test(4 votes)
- why are some questions easy and some are hard(4 votes)
- Now I can round better.!(3 votes)
- on the last quiz i had to do it like 10 times(3 votes)
- what does it mean to regroup(3 votes)