In first grade, the CCSS (1.NBT.C5) asks that students be able to mentally find 10 more or 10 less then a given number. It specifically states that students should not have to count, but that they also should be able to explain the reasoning used. The Common Core also emphasizes that students have a conceptual understanding, which means they learn math without having to learn "tricks". In this lesson, students explore how numbers change when they repeatedly add 10. This sets students up to later understand how to mentally find 10 more.
Students also apply MP7 and MP8 throughout this lesson. Students notice the structure of the number and then use repeated reasoning to help themselves solve future problems.
Review Past Learning:
We have worked with 10 all year. 10 is our best friend! Today we are going to look at another way we can use 10-by adding 10 over and over.
Connect to the Real World:
This is important because grown ups use adding 10 to help them add things quicker. For example, if I have $24, and then I get $10, I don't count on to figure out how much money I have. I use what I know about adding 10s to make it easier to solve.
Your thinking job today is: How does the number change when I add 10 over and over?
Present Task: Today we are going to enter the world of Woody and Buzz. Andy, their owner, is getting a bunch of new toys, but only if he does his chores. He gets 10 new toys everyday! We are going to figure out how many toys he has at the end of every day.
Problem 1: Andy has 15 toys in his toy box. He gets 10 more on Monday for doing his chores. How many toys does he have now?
I'll choose one person to come and model this problem with base 10 blocks. Other students will get to solve later!
Problem 2: Now Andy gets 10 more on Tuesday for doing his chores. How many toys does he have now?
Partner solve: I'll give students base 10 blocks to show how to solve this problem.
See the attached Class Chart for what our anchor chart looked like!
Present Task: At first, Andy had 15 toys. He got 10 more, now he has 25 on Monday. He got 10 more on Tuesday and now he has 35. I'm wondering how many Andy will have if he gets 10 more on Wednesday.
Make a prediction: How many will Andy have on Wednesday? What pattern do you see in these numbers? Listen to this Predicting the Next Number Partner Talk about what number they predict and why!
Prove it! I'll have one student show how they are sure 45 comes next.
Partner talk to summarize: Why did 45 come next in this group? How did the numbers change in this chart: 15, 25, 35, 45?
Students get a start number (decided and written in by teacher) to start with. They use the Toy Box mat for their base ten models and show how Jack gets 10 more toys every day.
Group A: Intervention
This group should start with a number under 10. These students also need to scaffold of base 10 blocks throughout. They may revert back to adding 10 ones. If that is the case, I'll ask: Is there another way we could represent 10?
Group B: Right on Track
Students get a number in the teens to start with. They have base ten blocks available.
Group C: Extension
Students start with a number in the twenties. They have base ten blocks available, but they may be able to do this mentally. If that is the case, make sure they can explain the reasoning of how they figured out 10 more, as this is explicitly stated in the standard.
One of the strategies I sometimes get is "I went down on the hundreds chart"-while this does work, I want to always make sure students have a conceptual understanding of why "going down" on the chart works. To scaffold this conversation, I'll ask: What is happening to the number when you move down the hundreds chart? How does that show you are adding 10?
Toy Story Inventory.pdf is attached!
Student Work Examples:
I saw a variety of strategies from students during this activity. I listed them below-click on the link to see the picture of a student using that strategy. I listed the strategies from most concrete (students use concrete models to solve) to most abstract.
I'll close the lesson by having students apply what they did today to a novel problem. This is just an equation-no story attached to it. Students are asked to show 2 strategies to solve 48 + 10. The 2 strategies is intentional-I am hoping students will show the pattern that they saw in today's lesson as one of their strategies. I am anticipating that the other strategy they will show will use a base 10 model.
This problem also gives me some data to use as I differentiate for the next day's lesson.
Closing Problem Toy Story is attached!
Lesson image is copyright Disney/Pixar and is from the Toy Story movies. Thanks to Pixar Planet for linking to this image!