Addition through 100 crossing tens

General

Students can add beyond 100 crossing tens.

Common core standard(s)

2.NBT.B.7
2.OA.A.1

Relevance

It is important for students to be able to add beyond one hundred so they can determine larger totals and as preparation for addition within one thousand.

Introduction

First practice with the number line to 100 by asking students to write a random number between 1-100. They then must hold their number and in silence form a number line with their classmates. Then ask a student to count beyond one hundred and check their counting by erasing the grey boxes on the interactive whiteboard.

Development

First discuss the importance of being able to add beyond one hundred. Then explain the example addition sum given by telling students that they can add to one hundred and then count on. This learning goal is presented in three ways, visually, in the abstract, and in story problems. Teachers can select the explanation that best fits their classroom needs by using the menu in the bottom right of the page. The explanation starts visually. Explain, using the blocks that you first count how many you have, then how many are being added, and add them together. Have students practice with the problems with blocks and ten frames. Then explain in the abstract. Tell students that they can solve the abstract addition problems by adding to one hundred first, and then to calculate with the rest of the addend. This can be done on the number line or without the number line. Students can also split the addends into tens and ones to add the tens and ones separately. Have students practice a method that they like with a few addition problems. Then discuss story problems. The steps of how to solve a story problem are given- determining what kind of problem is represented, which numbers are needed, saying or writing the math problem, and then solving the problem. Practice a story problem to check for their understanding.

Check that students understand addition beyond 100 crossing tens by asking the following questions:
- Why is it useful to be able to add beyond one hundred?
- What is useful to do when calculating beyond 100?

Guided practice

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

Closing

Discuss with students what the goal of the lesson was and ask them to solve a visually supported, an abstract and a story addition problem.

Teaching tips

Students who have difficulty with adding beyond 100 can be supported by making use of the number line. They can also make use of manipulatives like blocks to use during calculation.