Put Our Hands Together for Adding Tens

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SWBAT add tens to decade numbers within 100 by recognizing how the digit in the tens place is changing.

Big Idea

My students need to apply their understanding of place value to properties of addition and subtraction. We start to build that understanding today by connecting to addition facts they already know well.

Rev Them Up

5 minutes

I will use my game of, "Around the World," to review counting by 10's to get us thinking about the decade numbers.

I will have two students stand up, and I will ask: What number comes after 20 if I am counting by 10's?

The winner will be paired with another student and we will keep the game going until everyone has had a turn.  I will continue the same types of questions all the way to what comes after 110 when counting by 10's.

Whole Group Interaction

10 minutes

Students must develop a strong understanding of place value to use tens and ones to assist in addition and subtraction of 2-digit numbers. The CCSS want first graders to build the knowledge of place value to be able to complete addition and subtraction with 2-digit numbers. This requires being able add the ones to the ones then the tens to the tens in an equation.  This lesson will allow my students to use their understanding of the base-ten system to solve addition problems (1.NBT.C.4). Students use numbers as symbols to represent a problem, solve it, and explain their thinking. 

I will use base ten blocks to review with my students in adding tens to numbers. I will present several problems to them and use a dry erase board to show the digits. I will have them help me put the correct quantity of base tens on display and then add them together.

For example: Students, I need to solve 30+20; how many base ten blocks do I need to start with? (3)

How many more do I need? (2 more)

How many is that altogether? (10, 20, 30, 40, 50)

I will write our answer on the board.

My goal is for my students to identify the simple addition that is occurring in the tens place. They have become fluent in adding within 10, and I want them to see how adding the tens digits to solve this kind of problem simplifies it into something they already know well.

Independent Practice

10 minutes

I went here to access a worksheet for my students to independently practice adding tens within 100. This site, www.TLSBooks.com, has great practice sheets to access and use for students to gain stronger skill in many math areas. I want them to practice this skill to build their fluency of adding tens. Students must identify strategies to add two-digit numbers. When the the numbers are decade only with the ones place containing zeroes, it is easier for them to isolate the tens place and use simple addition strategies and look for known strategies such as: count up, plus ones, plus twos, doubles facts, etc. (1.NBT.C.4).

This student that has already begun using the counting up strategy to speed up his process, but my goal is for him to not have to count at all. I may need to use flashcards for addition within 10 for this student to build his fluency in addition. Now watch this student making connections. You will see I have some students who have already made the connection in adding tens. This is my goal for all of my students. 


5 minutes

I will close out today's lesson by having my students find a partner to share what they learned and how they solved their work.

Students I want you to stand up and push your chair in. I will count to 5 aloud. While I am counting, I want you to walk around the room. When I stop counting at 5, you have to have your partner in front of you. Ready 1,2,3,4,5. Okay I want you to tell your partner how you solved your problems today and what you learned about double digit addition.