Adding and Subtracting with Teen Numbers

Introduction

Welcome to today’s lesson on adding and subtracting with teen numbers! We'll explore how to work with numbers 11 to 19 in addition and subtraction. By the end of this lesson plan, your learner will confidently apply single-digit addition and subtraction facts to teen numbers, using various tools and strategies to understand and solve problems.

Before beginning the lesson, your learner should be able to partition teen numbers into ten and ones.

Key Concepts for Adding and Subtracting with Teen Numbers

• Ten and a Bit Structure: Teen numbers are composed of ten and an additional number, often referred to as "ten and a bit." This structure helps in simplifying calculations. For example, the number 13 can be broken down into 10 + 3.
• Addition and Subtraction Facts: Addition and subtraction facts within 10 can be extended to teen numbers. These facts include operations such as one more/less, making ten, and recognizing odd/even patterns.
• Applying Single-Digit Addition: Your learner can use their knowledge of adding single-digit numbers to add 13 + 2. Since 13 can be partitioned into 10 + 3, they can combine the 3 and 2 (3 + 2 = 5). Then, combine this result with the ten: 10 + 5 = 15.
• Applying Single-Digit Subtraction: Similarly, your learner can use their knowledge of subtracting single-digit numbers to subtract 19 - 3. Since 19 can be partitioned into 10 + 9, the three can be subtracted from nine (9 - 3 = 6). Then, combine this result with the ten: 10 + 6 = 16.

Teaching Plan

The following activities will help your learner become confident in adding and subtracting with teen numbers. Remember to go at a pace that is comfortable for your learner.

Examples and visuals to support the lesson:

1. Adding with Teen Numbers

Present your learner with first-then-now scenarios to link addition within ten to addition with teen numbers:

• "At first, Darren has three conkers. Then he finds two more. Now he has five conkers."
• "At first, Piya has thirteen conkers. Then she finds two more. How many conkers does Piya have now?"
• Show your learner equations to represent the story problems: 3 + 2 = 5 and 13 + 2 = 15. Discuss the connection between the equations, diagrams, and stories.
• Next, use tens frames and part-part-whole diagrams to show single-digit addition and the corresponding teen addition. For example, 5 + 1 = 6 then 15 + 1 = 16. Include examples that lead to a sum of twenty such as 8 + 2 = 10 then 18 + 2 = 20.
• You can also use number lines to demonstrate the connection between single-digit and teen calculations.
• Throughout the activity, repeat sentences like, "Three plus two is equal to five, so thirteen plus two is equal to fifteen."

Skill Check
I can use what I know about adding numbers up to 9 to help me add teen numbers.

2. Subtracting with Teen Numbers

Next, present your learner with first-then-now scenarios to link subtraction within ten to subtraction within twenty:

• "At first, the grocer had nine watermelons. Then he sold three of them. Now he has six watermelons left."
• "At first, the baker had nineteen cakes. Then she sold three of them. How many cakes does she have left?"
• Show your learner equations to represent the story problems: 9 - 3 = 6 and 19 - 3 = 16. Discuss the connection between the equations, diagrams, and stories.
• Next, use tens frames and counters to show single-digit subtraction and the corresponding teen subtraction. For example: 8 - 1 = 7 and 18 - 1 = 17.
• Use part-part-whole models and number lines, ensuring the focus remains on the connection between single-digit and teen calculations.
• Repeat sentences like, "Six minus one is equal to five, so sixteen minus one is equal to fifteen."

Skill Check
I can use what I know about subtracting numbers up to 9 to help me subtract teen numbers.

3. Practice and Challenge Tasks

Provide your learner with a variety of practice problems to reinforce the concepts in the lesson.

• Include missing number problems that vary the position of the missing number and the location of the equal sign. For example: 15 + 4 = __ and 16 = __ + 13.

For additional challenge, give your learner a list of general statements to determine if they are always true, sometimes true, or never true. For example:

• "If I add two to a number ending in three, I will get a number ending in five."
• "If I add two to a number ending in nine, I will get a number ending in zero."
• "If I subtract five from a number ending in seven, I will get a number ending in two."
• "If I subtract five from a number ending in zero, I will get a number ending in five."
• "If I subtract six from a number ending in zero, I will get a number ending in six."

Skill Check
I can solve different types of addition and subtraction problems with teen numbers.

Summary

Through this lesson plan, your learner will gain a solid understanding of adding and subtracting with teen numbers. By using visual aids, patterns, and language, they will confidently solve problems involving numbers 11 to 19. This skill will prepare them for adding and subtracting larger numbers and using advanced concepts such as borrowing and carrying.

Teaching Plan adapted from NCETM under OGL license v3.