Addition to 50 making ten with second addends <10

General

Students learn to add to 50 by making ten with second addends that are less than 10.

Common core standard(s)

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

Relevance

It is important to be able to add to 50, so you can combine larger amounts to know the total.

Introduction

Ask students to calculate the addition problem on the interactive whiteboard on the number line. You can choose to have them count out loud as you move on the number line.

Development

Discuss with students what the importance of adding to 50 is. The learning goal will be presented in three ways, visually, in the abstract, and a story problems. Choose the type of explanation that best works for your class by clicking on the menu in the bottom right of the lesson. In the visual explanation, use the visual support to count the objects. First count how many you have, then count to see how many more are added. Point out to students that you first make tens. You first count from 24 to the next tens, which is 6 to reach 30. You then count the 2 that you still have left. Your answer is 32. Practice doing this with the following images. In the abstract explanation, explain to students that there are different methods to add to 50 making tens. Using the number line, show how you first make ten, and then count 1 more. In the next slide, show how you count on the number line from 37. Show that you can use two methods. With explaining via story problems, refresh the steps of solving a story problem with the class and then walk through the steps of solving a story problem. Solve a few story problems with the class.

To check that students understand adding to 50 making ten with second addends less than 10 ask the following questions:
- Why is it useful to be able to add to 50?
- What is your favourite method to calculate totals of addition problems to 50?

Guided practice

Students first practice with addition problems with visual support. They then are offered an abstract addition problem without visual support and finally are given a story problem.

Closing

Check that students have understood the learning goal by asking how they calculate an addition problem to 50. Make sure to point out that one method is not better than another, but that they should use the one they like best. As a final exercise students solve the insect-problems. This can be done in different ways. Students can do this individually, or pairs/groups can select an insect to calculate the total tol. The insects can be dragged to make calculation easier.

Teaching tips

Students who have difficulty adding to 50 can first practice adding to 30. Use blocks or other manipulatives to help students visualize the addition process. Practice with problems that add 10, like 7+3, 6+4, etc. Next they can practice with making tens and then counting on with problems like 9+2, 8+3, etc. They can also make use of the number line.