10 More, 10 Less

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Objective

SWBAT use a strategy to add or subtract a ten within 100.

Big Idea

My class has been learning about place value and the meaning of tens and ones. This lesson will develop knowledge of adding or subtracting ten from a 2-digit number.

Rev Them Up

5 minutes

I will begin with reviewing what a set of ten looks like and have my students help me count. To get my students thinking about numbers and sets of ten I will have my students play a game of "Around the World."

Directions: This is a competitive game to see who can say the correct answer first.  You begin by selecting two students.  These students stand up and you will ask your question.  Whoever says the answer first, wins.  The winner is then matched with a new person and the same process proceeds.  You will continue to match the winner with a new person until everyone in the room has a turn and the final winner is produced. Go here to see a video of my class playing the game to compare numbers. Here my class is playing Plus/minus around the world version, but it can be changed to use other concepts.

Examples:

Okay, here we go, what is the answer to?

50-10=

30-10=

20+10=

60+10=

Continue with numbers like this until everyone has a turn. This activity will be a spring board for today's lesson. 

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 goal of today's lesson is to help my students be able to figure 10 more or 10 less by using their understanding of our place value system and without having to count (1.NBT.C.5).

To start, I want to help them identify the pattern that occurs on a 120 chart and how each column increases or decreases by ten as they move up and down.  Identifying this pattern will make it easier for me to point out to them how the tens digit changes by 1 going up or down.

I will be using a 120 chart for my students to be able to identify 10 more or 10 less. You can go here to print a 120 chart to use for this activity. I want them to have a visual to see the movement of the numbers, which this tool provides. Also, for my more concrete thinkers I will use base-ten blocks to help them see the values visually and be able to count using a concrete manipulative to check their thinking. For example, 56 is 5 tens and 6 ones, 10 less will take one rod away and we will have 4 tens and 6 ones leftover, or 46. 

I will have my students use a red, yellow and blue crayon to identify the pattern of 10 more or 10 less on the 120 chart. I will open up my Smart Board and pull up a 120 chart and complete this task with them while they do it at their desk.

Students find number 26 on the chart and color it yellow. Now if we have ten more, lets count ahead ten spaces and see what number we land on. We landed on 36, color it blue. 26+10=36. Now lets put our finger back on 26 and count back 10 spaces and find 10 less. We landed on 16, color it red. 26-10=16. 

I will continue to follow this process to help my students identify the pattern on the 120 chart and how the numbers are aligned.  Also, I will write the problems out and line up the digits to help them identify the change in the tens place.

Independent Practice

10 minutes

Print the worksheet and have your students keep the 120 chart out on their desk from our whole group interaction. I will have my students practice finding 10 more or 10 less on their own using the worksheet. I will walk the room and assist students who are having difficulty. If anyone is struggling with the 120 chart, I will exchange it for base-ten blocks to help them to solve their problem a different, even more concrete way.

The worksheet is providing them with several problems to solve for 10 more or less. I have three main ability groups for this concept at this time. About a fourth of my students have caught on to the pattern that when adding or subtracting 10, the tens place is changing by one more or one less. These students are using mental math. Half of my students still need the support of the 120 chart and are able to move across the numbers to find their answer and write it down. The other fourth of my class still need the support of concrete manipulatives, and I supply our base ten blocks for them to build their problems and then remove a ten rod to find their answer. I will have my lower students continue to practice this skill during centers time, and I am confident that, with more practice, they will progress to the higher stage.

Closing

15 minutes

I will close out today's lesson by conducting a think-pair-share discussion on today's objective.

Students, I am going to give you time to think about today's math. What method did you use to solve your problems? Explain what you did. Then, I am going to let you pair up with partner. I will set our timer and give you 2 minutes to talk with your partner about the way you solved your problems today. Then, we will meet our carpet and each pair of partners are going to have an opportunity to share with the class what they learned from today's objective.