# Adding up to 4 Two-Digit Numbers

Learning how to add up to 4 two-digit numbers is a second grade Common Core math skill: 2.NBT.6. 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.6 - Add up to four two-digit numbers using strategies based on place value and properties of operations

Students who understand this principle can:

1. Add using number lines, base-ten blocks (or the like), and hundreds charts.
2. Add up to 4 two-digit numbers.
3. Explain various methods for adding multiple two-digit numbers.
4. By citing place value and the properties of operations, explain why addition and subtraction strategies work for adding 4 two-digit numbers.

Video 1: Finding Costs of Pet Supplies: Adding using Place Value

This video starts by asking the provocative question, “How much does owning a pet cost?” Afterall, pets need lots of supplies. The video then provides a brief review of math facts relating to numbers, place value, and adding before exploring the above question.

In this video, your students will learn how to add up to 4 two-digit numbers by using place value.

Brief Math Facts Review:

1. Reviews place value by looking at a place-value chart.
a. In the number 267, 2 is in the hundreds place and represents 200.
b. 6 is in the tens place and represents 60.
c. 7 is in the ones place and is just 7.
2. Reviews that numbers can be represented in different ways.
a. 3 tens and 2 ones is the same as 2 tens and 12 ones.
b. Both represent 32.
3. Reviews that addends can be grouped in any order to get the same sum.
a. 2 + 2 + 3 is the same as 2 + 3 + 2
b. A common misunderstanding students often have is thinking that numbers must be added in order.
c. But 6 dogs + 4 dogs is the same as 4 dogs + 6 dogs.

After, the video turns to its core lesson, looking at how much owning a dog costs. The crate costs \$59 dollars, the collar \$17, the leash \$25, and the toys \$43. To solve, use place value to add the numbers.

1. 59 + 17 + 25 + 43 = ?
2. Starting with the tens place, you can add 50 + 10 + 20 + 40.
a. Rearranging the addends, you can add 10 and 40 to get 50.
b. 50 + 50 = 100, and 20 more equals 120.
3. Now we add the ones: 9 + 7 + 5 + 3.
a. Adding 7 and 3 equals 10.
b. Then 9 + 5 = 14
c. 14 + 10 = 24
4. Now, 120 and 24 are the partial sums; add them to get 144.
5. It costs \$144 for dog supplies.

The video then follows the same process for supplies for a fish and a hamster.

Fish: The tank costs \$65, the plants \$22, the pump (filter) \$30, and more fish \$37.

1. Adding tens: 60 + 20 + 30 + 30.
a. Add two at a time, and get 80 + 60.
b. 8 tens plus 6 tens equals 14 tens, so 80 + 60 = 140.
2. Adding ones: 5 + 2 + 7. The 0 can be ignored as there are no ones there.
a. 5 + 2 = 7
b. 7 + 7 = 14
3. 140 and 14 are partial sums; add them to get 154.
4. It costs \$154 to get these fishies.

Hamster: The cage costs \$25, the wheel \$8, the bedding \$7, and the water bottle \$11.

1. Adding tens: 20 + 10 = 30.
2. Adding ones: 5 + 8 + 7 + 1
a. 7 + 1 = 8; then, 8 + 8 = 16
b. 16  + 5 = 21
3. 30 and 21 are partial sums; add them to get 51.
4. The hamster supplies will cost \$51.

The video ends, reminding students what they have learned.

Video 2: Presents and Shopping: Adding Several Numbers

The video starts with Boddle introducing what the students will learn: how to add up to 4 two-digit numbers. First, we look at a few practice word problems.

“Jane is celebrating her birthday. She received 2 gifts from her neighbors, 12 gifts from her classmates, and 3 gifts from her family. How many gifts does she have in all?”

To solve this, we must place the numbers in a column.

1.       2
1 2
+   3   Add the ones side first.
1. We have 2 + 2, which equals 4.
2. And then we add 4 plus 3, which equals 7.
a. Note we added 2 numbers at a time to make it easier.
3. Then we move to the tens place, which only has 1, so we bring it down.
4. Jane has 17 gifts in total.

The next problem states, “Leo shopped for some clothes. He bought a jacket for \$32, a shirt for \$10, and a pair of socks for \$2. How much did he spend in total?”

To solve this, we must place the numbers in a column.

1.     3 2
1 0
+     2  Add the ones side first.
1. We can skip the 0, and simply add 2 + 2, which is 4.
2. Next, we move to the tens place.
3. 3 + 1 = 4
4. Leo spent \$44 in total.

After, Boddle moves on and has students practice adding 4 numbers. The first problem is 18 + 22 + 5 + 15. Like before, writing the numbers in a column helps.

1. First add the ones: 8 + 2 + 5 + 5
a. 8 + 2 = 10
b. 10 + 5 = 15
c. 15 + 5 = 20
2. We can only write one digit per place value, so we bring the 0 down, and bring the 2 to the tens place.
3. Then, add the tens, including the new 2.
a. 2 + 1 = 3
b. 3 + 2 = 5
c. 5 + 1 = 6

Before Boddle leaves, she gives a few helpful reminders. When adding several numbers,

1. Write the numbers in a column;
2. Add the ones first, making sure to add 2 digits at a time–then proceed with the tens;
3. Only 1 digit can be written per place value.

That’s the end of the lesson. See you next time!

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