# Using the Number Grid to Add or Subtract Ten

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## Objective

SWBAT add or subtract ten to/from a 2 digit number.

#### Big Idea

The Number Grid Challenge. Students will play a game that requires them to add or subtract ten from a number using the number grid. They will record their results using standard notation.

## Warm Up

10 minutes

I start the lesson by gathering the students on the carpet.  I want to review the concept that we have been working on (adding and subtracting 10 from a number).

"Who can remind us of what we have been focusing on?  Yes, that's right adding and subtracting 10 from a number.  I want to use the string of 100 beads to count from 1 and add 10 each time."

There is a video in the section resource that captures this discussion.

In this case the students are able to use a visual to model what happens every time a group of ten is added to the number one.  The students are learning to add a group of ten to one and two digit numbers and are able to explain why we say 41 when we have 4 groups of ten and a one (CCSS.MATH.PRACTICE.MP5 & CCSS.MATH.CONTENT.1.NBT.B.2).

## Introducing 100 Grid Challenge

15 minutes

Advanced Preparation:  You will need to make copies (for your class) of the 100 Grid Challenge recording sheet.  You will also need colored chips, a +10/-10 spinner and a 100 grid for each team of two.

I have the students face the large number grid as I introduce the next activity.  There is a video in the section resource that models this introduction.  The video is about 5 minutes but it gives a good visual of how to introduce and play the game.

"I want to introduce you to a new game today.  It is a game that will require you to add or subtract ten from a number.  I need a volunteer to help me model this game.  To play each player will need 6-8 colored chips. Each player must have all of one color and the other must have all of a different color.  To start, we will each place our chips over different numbers on the 100 grid and we will each have a recording sheet.  One player will then spin the +10 or -10 spinner (you will need to make these) and then either add ten or take 10 away from a number that one of their chips is covering.  That player then records their equation in the +10 or -10 column on their recording sheet. The next player then repeats the process for their turn.  Then game is over when one column is filled on a recording sheet.  The only rule is you can't move a chip that would require you to go off the game board (i.e. +10 to the number 98)."

The students are learning to add or subtract ten from any 2 digit number and then write an equation to represent the "action" of their move (CCSS.MATH.CONTENT.1.NBT.C.4 &  CCSS.MATH.PRACTICE.MP4).

## Playing the Game

30 minutes

Students are now put into teams of two and play the game with each other.  They will each need a recording sheet and I suggest that you have extra for them to play a 2nd round.  It is important that the players know to check each others work.  It is important for peers to critique each others thinking and make conjectures about each others ideas (CCSS.MATH.PRACTICE.MP3).

## Formative Check In

10 minutes

As a quick check in, I ask each student to complete the formative task in the section resource.  This task will allow me to see who well students are adding and subtracting 10 to a number, without using a number grid or number line.

It is IMPORTANT to try and watch who students are solving the problems.  If you just collect the finished sheets, you will not see who they are figuring out the answer.  You want to know who is understanding that you just adjust the tens column by 1 and  who is using a different method for solving.

## Continued Practice

5 minutes

I will ask the students to meet me on the carpet and hand out their sheet for today's Mad Minute exercise.  This routine was introduced in a previous lesson.  Please check out the link to get a full overview of this routine.

I want to really focus on fact fluency and build upon the students ability to solve within ten fluently (CCSS.MATH.CONTENT.1.OA.C.6).  I am going to use the Mad Minute Routine.  This is a very "old school" routine, but I truly feel students need practice in performing task for fluency in a timed fashion.  Students need to obtain fact fluency in order to have success with multiplicative reasoning.  Students who don't gain this addition fact fluency by the end of 2nd grade tend to struggle with the multiplicative reasoning in third.  Having this fluency also allows them to work on more complex tasks because the have the fact recall to focus on the higher level concepts.