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Lesson 9: Addition and subtraction word problems

# Addition, subtraction, and estimation: FAQ

## 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.