# How Many On My Plate? (Subtraction)

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## Objective

SWBAT subtract ten to any given number. SWBAT add or subtract a multiple of 10 to any given number and represent the action with an equation.

#### Big Idea

Students will use their ability to count by tens on and off the decade by taking part in an activity that requires them to start with a number of cubes and then repeatedly subtract ten.

## Warm Up

10 minutes

Advanced Preparation:  You will need enough white boards, markers, and erasers for each student.

"I would like each of you to grab a white board, marker and an eraser and sit on the carpet.  I am going to say a number.  I want you to listen to the number, add ten to that number, and then write the new number on your board.  I want you to keep the board against your chest so that no one else can see your answer.  I will then ask everyone to turn their board toward me so that I can see your answer."

There is a video, in the section resource, that models this procedure.

In this activity, the students are meeting the CCSS expectation of mentally finding 10 more or 10 less than a number, without having to count and are able to explain their thinking (CCSS.MATH.CONTENT.1.NBT.C.5).

## Introduction to How Many On My Plate? (Subtraction)

10 minutes

Advanced Preparation:  You will want to print off 4-6 copies of the "How Many On Your Plate? (Subtraction) form."  You can find this in the section resource.  You should then fill out that ten will be taken away for each day and you should choose a starting number for each set.

"Today we are going to play "How Many On Your Plate" (like we did yesterday), but we are going to change it from adding ten to subtracting ten on each day.  You should look at the starting number and build that number on our plate (with cubes).  Then you can take away ten each day. Like yesterday, you will fill in the number on your plate after each day."

There is a video in the section resource that models this introduction.

This activity meets the CCSS expectation because the students are subtracting multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90, using concrete models and using strategies based on place value to explain their reasoning (CCSS.MATH.CONTENT.1.NBT.C.6).

This lesson is more difficult then the previous lesson because it involves subtraction and the idea of counting back or down.  Some students may see the relationship to addition and use that concept to find the solutions.  However, other students may need adaptation (see activity in the reflection of the next section).  It is important to make sure students use some form of a manipulative to represent the ten begin taken away.

## Station Time

40 minutes

The students can start with one of two activities. However, I do explain to them that they should try to get to both of them during the station time. I will give them a signal for when to switch.

• What's On My Plate Subtraction:  This activity was just introduced in the previous section.
• +10 or -10:  This activity was introduced in the previous lesson.  My students started this yesterday and will continue working on their packets today.  If you need to see a detailed description or obtain the resource sheets, you should read the Introducing New Activities section of the linked lesson.

As students are working on these activities, you will want to circulate to see how students are adding or subtracting tens.

Are they . . .

• building each number and then adding or subtracting ten?
• building the first two numbers and then recognizing the pattern?
• able to mentally add or subtract or just understand that they change the tens column by one number?

In both of these activities, the students are modeling their results with numbers and/or equations (CCSS.MATH.PRACTICE.MP4).

## 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.