Unknown Addends Part 2

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SWBAT determine the unknown whole number in an addition equation.

Big Idea

My First Graders have been studying many addition strategies. Today, they will use these strategies to determine an unknown number in an addition equation.

Rev Them Up

5 minutes

I want my students to get their minds thinking about math, especially addition and subtraction. This will help them with today's lesson to solve for unknown addends. I will have them play a game of Around the World with subtraction and addition facts. One great thing about the Around the World game is that it encourages fluency, which helps when solving complex word problems.

Have two students stand up and verbally state a problem to solve. Whoever says their answer first is the winner and that person is then matched to a new person. The competing continues around the room until the final winner is left. I will be alternating between addition and subtraction problems such as;





Whole Group Interaction

10 minutes

There are multiple strategies that can be used to solve an unknown addition equation. I used a concrete method to explain, teach, and hopefully reach all of my students during this previous lesson.  I have several students who are able to use counting up and/or math fact fluency to solve for unknown whole numbers in an equation. (1.OA.D.8). But introducing this concept with a concrete connection helps all of my students to see the connection with using an x for the unknown. I will review solving for an unknown addend by writing 3 problems on the board:




I chose one problem that they could use a doubles fact to solve for the unknown and one problem that would use Zero the Hero. My students are beginning to see how all the strategies they have learned help them solve different problems and they will use that knowledge here.  Check out our discussion here. Questions I will ask:

How can we solve the first problem? (counting up, subtracting 6-2) Why does that strategy help solve the problem?

What do we know that will help us figure out question #2? (we know that 6+6=12, so the missing number is 6) How do you know that?

What do we know about problem #3? (any number added to a zero equals that number) What is missing? How do you know that?

These questions will help deepen student thinking and continue to develop their ability to express themselves clearly and precisely using correct mathematical vocabulary. Allowing discussions like this, makes them eager to share because the environment encourages them to express their ideas and arguments. (MP3). 


Independent Practice

15 minutes

I will have my students practice solving for an unknown whole number in an addition sentence using the printable unknown addend activities. I will have my students cut apart their cards and throw away their trash. I will pass out large construction paper and ask my students to go through and match each problem with its answer and glue them together on the paper. You will notice my students used a slightly different match-up activity then the one you will print. The online activity expired and I created one for you to print and use. My students had to organize their game pieces to match missing addends to their problems. After the matching is complete, I will have them use the second part of the activity to solve for the missing addend. This sheet will allow additional practice and you should encourage them to be solving with a strategy and using the relationships they know about numbers.


5 minutes

I will call my class back together at the carpet and have a discussion identifying strategies they used to solve problems. I will make a list on the board of the different ideas they give me for solving for an unknown addend.