# What's Under the Sheet? Part,Part, Total Within 10 and 20

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## Objective

SWBAT solve a problem in which the total and one part are known. SWBAT use relationships among different combinations of numbers up to 10.

#### Big Idea

Don't sweep it under the rug but rather hide it under the sheet. Today students will play a missing addend game called What's Under the Sheet.

## Warm Up

10 minutes

Before the students arrive for math class, I have posted the question, Would you rather have a sunny or snowy day?, on the whiteboard.  As students come into the room, I ask them to gather by the board.

"Who could read the question that is on the board?  I now want you to come up and fill in a tally mark for the type of day you rather have."

The question itself (as far as content) is not connected to anything and you can create what ever question you desire.  The important part is the discussion that follows.

There is a photo in the section resource that shows the answers that were given during the discussion.

"How many people chose sunny?  How many people chose snowy?  Who could give me an equation that represents what we found?  Who could give me an expression about the data (looking for use of the < or > sign)?  The students are expected to be able to compare two numbers using the <,>, or = sign by the end of first grade (CCSS.Math.Content.1.NBT.B.3).  How many people answered the survey?  How do you know?  Who can give me an 'I Notice" statement about the information?"

"Look how much information you gave me about the data we collected."

## Introducing What's Under the Sheet?

15 minutes

Advanced Preparation:  You will need a piece of construction paper for each team, connecting cubes, and a recording sheet for each team member.  The recording sheet can be found in the section resource.

"Today, we are going to play a game called "What's Under the Sheet?"  It will involve you using strategies to find out how many cubes are hidden under the sheet.  You will be doing the work of master mathematicians and solving for what mathematicians call the unknown."

I then introduce the game to them and model it by playing with another student.

"You will start by grabbing any number of cubes between 8 and 12.  You will choose one person to go first and they will be the person that hides the cubes first.  Once you have filled out the total number of cubes you are starting with (on your recording sheet), you will then hide some cubes under the sheet (construction paper) and leave some showing on top of the sheet.  Let's say that you start with ten cubes.  You put 6 under the sheet and four on top.  Your partner will then fill out how many cubes are not hidden, leave the hidden space blank and then write the equation

___ + 4=10 or 10=____+4.  Then that person tries to figure out how many cubes are under the sheet and describes how they figured it out.  Then he/she fills in the missing part on the recording sheet."

There is a video of the students playing this game in the section resource and a photo of a completed recording sheet.

In this activity, students are determining the unknown whole number in an addition equation (CCSS.Math.Content.1.OA.D.8).  This is a complicated skill and must be worked on throughout the year in order for students to develop a sound understanding and mastery by the end of the year.

## Station Time

30 minutes

During station time the students can choose from any of the following three station activities.

1.  What's Under the Mat?:  This activity was just explained in the previous section.

2.  10 Sticks:  This activity has students using a set of ten beads (5 white and 5 red).  The students sit knee to knee or across from each other and one person holds the stick in his/her hand.  The student then hides some of the beads and flashes the remaining beads.  The other student then must guess how many beads are hidden.  There is a video of the students playing this game int he section resource.

3.  Flashing Ten Frames:  This activity was introduced in a previous lesson.  Once you click on the link, you will need to read the Now You See It, Now You Don't section of the lesson.  The resource cards are also in that section's lesson resources.  There is also a video (in the resource section on the side) that demonstrates how to conduct this activity. *Note: the audio on this video is really low but you will be able to see two kids working with each other.

All three of these activities have students practicing their fact fluency within 10.  The Core Standards expect students to be fluent with these facts by the end of first grade (CCSS.Math.Content.1.OA.C.6)

## Lesson Wrap Up

10 minutes

I end this lesson with a discussion about using 5+5 to reason about combinations of 10.

I ask the students to meet me on the carpet in a circle.  This way everyone can see and be part of the discussion.

"I want you to look at my 10 stick (I show them the 5 red and 5 white beads int he stick).  How many beads are there all together?  Can we all agree that there are ten beads?  I am going to hide some of the beads in my hand and then show you some of the beads (much like some of you did today during the station time).  I then hide 3 beads behind my hand and show them 7 beads (5 red and two white).  How many beads are behind my hand?  Why do you think that 3 are hidden?  How did you figure it out?"

You want to ask students to share their strategies for figuring out how many beads were hidden.  Students will offer suggestions like: Using Fingers, Just knowing the 7+3 fact, counting on from 7, there were 5 red and 2 white.  2+3=5 so there must be three hidden.

"I want to focus on this last example.  How did knowing that there were 5 red and 5 white beads help you find the amount hidden?"

You are looking for someone to connect that there were 2 white showing and that 2+3=5.

## Continued Practice

5 minutes

I end this session by hang students complete compliments of 10 or 20 sheet (based on each students need).  These sheets are both found in the section resource.  I am focusing on the students ability to determine the unknown whole number in an addition equation by relating three whole numbers (CCSS.Math.Content.1.OA.D.8). The students are demonstrating their ability and competence with this CCSS expectation.