Adding and Subtracting 1

Introduction

In this lesson plan, we will focus on developing fluency in adding and subtracting 1 by exploring the concept of "one more and one less." We will use engaging story problems, visual models, and equations to reinforce these fundamental arithmetic operations. By the end of this lesson, your learner will be able to confidently solve addition and subtraction problems involving the concept of changing a number by one.

Before beginning the lesson, your learner should be familiar with the concept of one more and one less.

Key Concepts for Adding and Subtracting 1

Here are a few concepts that are helpful to know for this lesson.

• One More and One Less: "One more and one less" refers to the concept of counting forward by one or counting backward by one, respectively. For example, when counting forward, adding one to a number results in the next number in the sequence. Conversely, counting backward involves subtracting one to move to the previous number.
• Parts of Addition Equations: Addends are the numbers being added together in an addition equation. The sum is the result or total obtained by adding the addends together. For example, in the equation 3 + 1 = 4, the addends are 3 and 1, and the sum is 4.
• Parts of Subtraction Equations: The minuend is number from which another number is subtracted. The subtrahend is the number that is subtracted from the minuend. The difference is the result obtained by subtracting the subtrahend from the minuend. For example, in the equation 5 − 2 = 3, the minuend is 5, the subtrahend is 2, and the difference is 3.

Teaching Plan

The following activities will help your learner develop fluency in adding and subtracting 1. 

Examples and visuals to support the lesson:

1. Counting and Identifying One More and One Less

Use this activity to review and assess your learner's ability to recognize numbers that are one more and one less.

• Begin by reviewing counting between 0 and 10 on a number line. Tap the numbers as your learner counts forward and backward.
• Then review "one more" and "one less". Ask your learner, for example, "What is one more than four? What is one less than four?" Encourage your learner to use the following stem sentences: "One more than ___ is ___. One less than ___ is ___."
• Have your learner practice filling in missing numbers on number lines and in number sequences. Practice until your learner is fluent in identifying one more and one less without counting.

Skill Check
I can find numbers that are one more and one less without counting.

2. Writing Equations with Adding 1

Next, progress to writing and solving addition equations with an addend of one.

• Start with a first-then-now addition story such as: "First there were three flowers in the vase. Then one more flower was added to the vase. Now there are four flowers in the vase."
• Then start to include part-part-whole contexts. For example, "There are three footballs and one basketball. There are four balls altogether."
• Use representations such as concrete objects, pictures, and ten frames to model the stories. Have your learner write the equation as they tell each story.
• Draw attention to the fact that the sum is always one more than the starting addend. Work towards the generalized statement: "Adding one results in one more."

Skill Check
I know that adding one is the same as finding one more.

3. Solving Equations with Adding 1

Now move on to equations where the first addend is one. This activity will also reinforce your learner's understanding of the commutative property of addition.

• Show a pair of equations with the sum of the second equation missing. For example: 3 + 1 = 4 and 1 + 3 = ?. Make sure that your learner recognizes that the addends in each equation are the same but in a different order.
• Challenge your learner to solve the second equation using their knowledge of the commutative property. Remind them: "If we change the order of the addends, the sum remains the same."
• Once your learner has "predicted" what the sum will be, model the equations with counters or diagrams to show whether their solution is correct.
• Provide your learner with several addition equations where an addend is 1. Have your learner find the sum for each equation.

Skill Check
I can use what I know about adding 1 to solve problems no matter what order the addends are written.

4. Equations with Subtracting 1

Once your learner is able to fluently add one, move on to subtracting one.

• Begin with first-then-now subtraction stories such as: "First there were eight donuts. Then one was eaten. Now there are seven donuts."
• Next, include part-part-whole contexts such as: "There are eight children. One child has a balloon. Seven children do not have a balloon."
• Just as with the addition stories, use objects, pictures, and math tools to model the stories. Have your learner write each equation as they tell the story.
• Point out that the difference is always one less than the minuend. Work towards the generalized statement: "Subtracting one results in one less."
• Provide several subtraction equations where the subtrahend is one. Have your learner find the difference for each equation.

Skill Check
I know that subtracting one is the same as finding one less.

5. Varied Practice

Next, provide varied practice that includes both addition and subtraction of one. Present problems that have a missing number in subtraction equations, on number lines, on part-part-whole diagrams, and as story problems.

Summary

In this lesson plan, your learner has practiced developing fluency in addition and subtraction with 1 through the concept of "one more" and "one less." With the use of story problems, equations, and visual models such as number lines and part-part-whole diagrams, your learner has gained a deeper understanding of how to manipulate numbers by adding or subtracting one.

Teaching Plan adapted from NCETM under OGL license v3.