Addition to 100 crossing tens with addends >10

General

Students learn to add to 100 crossing tens with addends greater than 10.

Common core standard(s)

2.NBT.B.5
2.OA.A.1

Relevance

It is important for students to learn to add to 100 crossing tens so that they learn how to calculate total amounts of larger amounts.

Introduction

First practice on the number line by asking students to drag the balloon with a number to where it belongs. Then practice with to addition problems on the number line to 50 with and without crossing tens.

Development

First discuss the importance of being able to add to 100 and explain how to cross tens. Next the learning goal will be explained in three ways, visually, in the abstract, and in story form. You can select the explanation that best suits your classroom by clicking on the menu in the bottom right of the lesson. With the visual explanation, start by counting the objects. Explain how you can add the two addends together. Have students practice a few visual problems to check that they understand how to add with visual support. Next are the abstract addition problems. They are presented in a variety of methods. First show students how they can add the numbers by taking steps on a number line. Show that they first add the tens and then the ones. Next show how, on the number line, you add to the next ten, and then add tens and then add ones. There are also two more ways given to solve the addition problem without the number line. With the story problem, students are given steps to use to solve the story problems. Check that students are able to follow these steps by solving the given story problem.

Check that students are able to add to 100 by asking the following questions:
- Why is it useful to be able to add to 100?
- What do you look at first when adding to 100?
- How do you regroup tens for example in the problem 58+23?

Guided practice

Students first practice an addition problem with visual support, then they practice without visual support and finally are given a story problem to solve.

Closing

Give each student a sheet of paper and tell them they will be making addition problems. They must first write a number between 1 and 50. They walk around the class, find a partner, and then solve the addition problem with their two numbers. Then half of the class writes a number from 10-20, and the other half from 20-80. The students must find a partner from the other half of the class and solve the addition problem with their two numbers.

Teaching tips

Students who have difficulty adding to 100 can be supported by the use of manipulatives. They can also be helped by writing out the addition problems on the number line.