Subtracting Consecutive Odd and Even Numbers

Introduction

In this lesson plan, we will explore patterns for subtracting consecutive odd and even numbers and use them to solve a variety of problems. We'll start by using engaging first-then-now subtraction stories where the minuend and subtrahend are consecutive numbers. Through these stories, we will visualize how subtraction affects the quantity and understand the resulting difference.

Before beginning the lesson, your learner should understand odd and even numbers and be proficient in subtracting consecutive numbers.

Key Concepts for Subtracting Consecutive Odd and Even Numbers

The focus of this lesson is to provide your learner with a strategy for subtracting numbers. By recognizing the patterns of subtracting consecutive odd and even numbers, they will be able to calculate the difference fluently. Here is a summary of the patterns covered in this lesson:

• Consecutive odd numbers have a difference of two. If we take the odd numbers 3 and 5 as an example, the difference between them is two (5 - 3 = 2).
• Similarly, consecutive even numbers also have a difference of two. For instance, 4 and 6 are consecutive even numbers with a difference of two (6 - 4 = 2).

Teaching Plan

The following activities will help your learner become confident in subtracting consecutive odd and even numbers. Be sure to work at a pace that is comfortable for your learner.

Examples and visuals to support the lesson:

1. Exploring First-Then-Now Subtraction

Start with a first-then-now subtraction story where the minuend and subtrahend are consecutive odd or even numbers. Write the equation as you tell the story, pointing out that "all except 2" are left.

Here are a few examples:

• First I had five apples. Then I gave three apples away. Now I have two apples. (5 - 3 = 2)
• First there were eight children playing a game. Then six children left. Now there are two children playing the game. (8 - 6 = 2)
• There were three colorful balloons for the birthday party. Then one balloon floated away. Now, there are two balloons left. (3 - 1 = 2)
• There were ten toy cars in the toy box. Then, eight toy cars were taken by the children. Now, there are two toy cars in the box. (10 - 8 = 2)

Skill Check
I can see the pattern for story problems that have 2 left.

2. Exploring Part-Part-Whole Diagrams

Next, explore part-part-whole contexts where the parts have a difference of two.

• Provide your learner with a variety of part-part-whole relationships where the whole and one of the parts are consecutive odd or even numbers.
• Represent them visually (using part-part-whole diagrams) and with equations. Your learner should identify that the other part is two.
• Work towards the generalized statements: "Consecutive odd numbers have a difference of two. Consecutive even numbers have a difference of two."

Skill Check
I can recognize odd numbers and even numbers that have a difference of two.

3. Solving Subtraction Equations

Once your learner understands the pattern, they can practice solving missing number problems.

• Provide your learner with equations to solve (without story problems). The equations should have a variety of numbers from 0 to 10 that result in a difference of two.
• After your learner recognizes that the difference is two, have them explain how they know their answer is correct.
• Next, provide several equations for your learner to sort into groups - those that have a difference of two and those that do not. This will help them to develop fluency in recognizing number pairs that have a difference of two.
• Continue to provide them with a variety of practice problems that involve subtracting two (such as 7 - 2) and that have a difference of two (such as 6 - 4).

Skill Check
I can use what I know about consecutive odd and even numbers to solve missing number problems.

Summary

With this lesson plan, your learner has explored subtraction with consecutive odd or even numbers and identified the pattern of numbers that have a difference of two. They learned that consecutive odd numbers and consecutive even numbers always have a difference of two. This understanding will help your learner solve subtraction problems efficiently and recognize number pairs that result in a difference of two.

Teaching Plan adapted from NCETM under OGL license v3.