Solving Story Addition and Subtraction Problems

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SWBAT use the counting on, counting back or known fact strategy when solving story problems. SWBAT accurately identify the action in the story problem. SWBAT accurately represent their thinking with an equation.

Big Idea

Students will all be asked to use specific strategies to solve a variety of addition and subtraction word problems.

Warm Up

10 minutes

I start the class by gathering everyone in a circle.

"We are going to use today's warmup to participate in a familiar activity.  I am going to ask you to work with a partner and play 10 sticks.  I am going to model a quick round of ten sticks to refresh your memory.  

I hold all of the sticks in front of me and then drop them on the floor/table.  Remember, I only want to hold them up a little bit so that the sticks don't go flying everywhere.  I then drop then figure out the total value by counting the 10's and the 1's.  Once I have counted them, I tell my partner how much the value was and how I would write that number.  So, if I dropped 6 tens and 4 ones, I would say 64 and then tell my partner how to write that number."

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

In this case the students are counting up to 100, starting at any number less than 100. and are able to express how a number of objects can be expressed with a written numeral (CCSS.MATH.CONTENT.1.NBT.A.1).

I will be playing this game during the next two lessons as we prepare to start our unit on 10 more and 10 less and counting on/off the decade. I just want to make sure everyone is clear on the game now before we head into that work.

*Differentiating Opportunities:  You can give student two sets of sticks, so they  have to count to 200.  You can use one set and ask students play the regular way but then ask them how many more to 100.

Solving Story Problems as a Group

15 minutes

During this section you will present a variety of story problems that will involve addition and subtraction.  I don't tell them which kind of problem it is ahead of time but instead encourage them to listen carefully and visualize the action.

"I am going to read you a variety of story problems today.  Using the routine that we have established (visualizing, identifying action, and solving) I want you to come up with a solution for each one.  We will work on these as a class and we will show a variety of ways for solving each one."  

Tom had 13 slices of pizza.  His friend came over for lunch and ate 6 of the slices of pizza.  How many slices of pizza were left?"

I then review the problem, have them retell it in their own words, and ask how they would solve the problem?  I ask for volunteers to dictate to me what they would do.  I record each idea on the whiteboard easel.  The students are meeting a CCSS math practice of explaining to themselves the meaning of a problem and looking for entry points to its solution (CCSS.MATH.PRACTICE.MP1).

*It is likely that someone will mention drawing a picture by drawing all of the slices and then crossing out the ones that were eaten.  Although this is a viable solution, at this point in the year I am now asking my students to find another way.  I want students to all move to the counting back strategy.  However, some have already moved past that and are using known facts or relational thinking (i.e. 6+7=13 so 13-6=7).  

There is a poster in the section's resources that models the approach of counting back with a number line and known facts.

Once you are finished with this first problem, you could also use these:

*Tim collects rocks along the river.  Yesterday he found 12 smooth rocks.  Today he found 3 more smooth rocks.  How many rocks did he find?

*Jan has 4 red fish and 3 yellow fish.  Her friend gave her 8 orange fish for her tank.  How many fish does she have?

Solving Story Problems Independently

40 minutes

Advanced Preparation:  You will need to copy a story problem packet for each student.

"You will now work on some problems on your own.  Some of you will not finish all of these problem and that is ok.  Your job is to use your time efficiently and to do your best with your work. Remember, you need to show your thinking and I really would like to see who you are moving away from the drawing all strategy with the subtraction problems.  I want to see who well you can count on or count back.  If you get stuck on a problem, I will help you with it."

As students are working and or as the finish a problem, you will want to notice:

  • Can students accurately make sense of the action in the problem?
  • Which strategy are they using to solve each problem?
  • How are they recording their thinking?
  • Are they accurate with their representations and answers?

I have included a video of a student explaining their approach to the 1st problem and two examples of different strategies being used.

In this case students are use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, and taking apart by using drawings  and equations (CCSS.MATH.CONTENT.1.OA.A.1).  The CCSS expect that first graders can effectively use efficient approaches to solve these types of story problems.  

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.  However, 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.