# Add & Subtract with 1000

Learning how to add and subtract within 1000 using different techniques is a second grade, Common Core math skill: 2.NBT.7. Below we show two videos that demonstrate this standard. Then, we provide a breakdown of the specific steps in the videos to help you teach your class.

Prior Learnings

Your students should be familiar with the first grade skill of counting up to 120 starting from any number below 120 (1.NBT.1), this skill helps them understand greater or less than values. The second grade skill is also closely linked to the first grade skill of understanding place values (ones and tens) in two-digit numbers (1.NBT.2).

Future Learnings

Comparing large numbers as greater than, less than, and equal to will help your students understand future concepts in third grade. In third grade, your students will learn how to interpret the products of whole numbers (i.e. 8 x 3 is the same as 8 groups of 3 objects each) (3.OA.1). They will also learn to use multiplication and division within 100 while solving word problems in situations that involve “equal groups, arrays, and measurement quantities” (3.OA.3).

Common Core Standard: 2.NBT.7 - Add and subtract within 1000, using concrete models, drawings, and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction

Students who understand this principle can:

1. Use models to add and subtract within 1000.
2. Explain how addition and subtraction are related, using it to solve problems.
3. Apply their knowledge of place value to add and subtract each place value.
4. Explain different strategies for adding and subtracting.
5. Utilize concrete models, drawings, and the following strategies to add within 1000: place value, properties of operations, and the relationship between addition and subtraction.

2 Videos to Help You Teach Common Core Standard: 2.NBT.7

Below we provide and breakdown two videos to help you teach your students this standard.

Video 1: Hop Along with Cricket on an Open Number Line

The video begins by asking students, “How do you add 514 + 253 using an open number line?” In this lesson, students will learn to add within 1000 using an open number line.

Before moving into the core lesson, the video provides a brief review of some math facts pertinent to the lesson.

1. Reviews that numbers can be broken down into place values using base-ten blocks.
2. Reviews the Commutative Property of Addition—numbers can be added in any order to find the sum.
3. Reviews that open number lines are tools that help visualize adding and can help count up by hundreds, tens, and ones. They also have no markings, allowing us to fill in the numbers as we count up.

After, the video moves straight into the core lesson: “Add 243 + 437” using an open number line.

1. When drawing an open number line, start with the biggest addend: 437.
2. Next, hop up by hundreds, tens, and then ones.
3. Hop by 200 first, landing on 637. Mark that point on the number line.
4. Next, hop up by 40, landing on 677. Mark that point on the number line.
5. The last hop is in the ones place, +3.
6. 677 + 3 = 680.

Your students just completed 243 hops in 3 easy steps, finding the answer: 243 + 437 = 680.

The video explains a common misunderstanding is that you can only hop based on place value from hundreds down to ones, but hopping up in a different order works too. The video shows this is true using the above problem, hopping up first by 3, then 100, then 100 more, and then 40, landing on 680.

Next, the video offers another problem: Solve 351 + ___ = 738.

Usually we start with the biggest addend, but in this case, there’s only one. So, we start with that and hop up the number line until we get to 738, which we can write at the end of the number line.

1. We can hop any order that makes sense.
2. 351 + 50 = 401, so we hop up 50.
3. Adding 300 to 401 makes 701, so we hop up 300 more.
4. Careful not to go over the answer, we can hop 30 more, making 731.
5. It takes just 7 more hops to get to 738.
6. Next, add together all the hops to find the missing number.
a. 300 + 50 + 30 + 7 = 387.
7. So, 351 + 387 = 738!

The video closes by reminding students what they have learned.

Video 2: Sending Letters and Solving Problems

This video covers adding and subtracting within 1000. First, for practice, Boddle helps some postmen send some mail.

Each mailbox has an addition or subtraction problem, and the answers are written on the envelopes. To put the correct letter in the mailbox, we simply have to match the envelope to the right mailbox.

1. The first mailbox reads 300 + 200.
a. The ones and tens place are 0 for both.
b. So we can simply add 3 + 2, which is 5.
c. Then we add the 0’s back to get 500.
d. We put the envelope with 500 into the mailbox.
1. The next mailbox reads 600 - 40.
a. The ones place for both numbers are 0.
b. So we can subtract 60 - 4, which is 56.
c. Then we add back the 0, making 560.
d. We place the correct envelope into the mailbox.
1. The last mailbox reads 428 + 196.
a. Start with the ones place, 8 + 6 = 14.
b. We can only write one digit per place value, so we bring down the 4 and put the ones in the tens place.
c. Adding the tens: 1 + 2 = 3 and 3 + 9 = 12.
d. 2 goes below the tens and 1 goes into the hundreds.
e. Adding hundreds: 1 + 4 = 5 and 5 + 1 = 6.
f. Therefore, 428 + 196 = 624.

Boddle recaps what we have learned in this lesson:

1. If the ones place value is 0 for both numbers, then solve the other place values first and add 0 at the end.
2. If both ones and tens place values are 0, skip them and proceed with the hundreds place. Then add back the 0’s.
3. In other cases, add one place value at a time, starting from the rightmost place value.

Hope this helps! See you next time!

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*Information on standards is gathered from The New Mexico Public Education Department's New Mexico Instructional Scope for Mathematics and the Common Core website.