Cracking the Code: Breaking Apart Numbers to Add!

Math Grades 1st Grade 4:47 Video
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Lesson Description

Learn how to break apart 2-digit numbers into tens and ones to make adding easier and faster! We'll use this cool trick to solve addition problems like a math wizard.

Video Resource

Breaking apart 2-digit addition problems | Addition and subtraction | 1st grade | Khan Academy

Khan Academy

Duration: 4:47
Watch on YouTube

Key Concepts

  • Place Value (Tens and Ones)
  • Decomposing Numbers
  • Adding Tens and Ones Separately

Learning Objectives

  • Students will be able to identify the tens and ones digits in a two-digit number.
  • Students will be able to break apart a two-digit addition problem into smaller addition problems involving tens and ones.
  • Students will be able to add the tens and ones separately and then combine them to find the total sum.

Educator Instructions

  • Introduction (5 mins)
    Start by reviewing what tens and ones are. Ask students to give examples of numbers and identify the tens and ones digits. (e.g., What is the tens digit in 23? What is the ones digit in 45?).
  • Video Time (7 mins)
    Show the Khan Academy video: 'Breaking apart 2-digit addition problems | Addition and subtraction | 1st grade | Khan Academy'. Pause the video at key points to ask questions and ensure understanding.
  • Practice Together (10 mins)
    Work through example problems on the board, guiding students through the process of breaking apart the numbers. For example, 24 + 32 = (20 + 4) + (30 + 2). Then add the tens (20+30 = 50) and the ones (4+2=6), and finally combine them (50+6 = 56). Use manipulatives like base-ten blocks if needed.
  • Independent Practice (10 mins)
    Give students worksheets with 2-digit addition problems to solve by breaking apart the numbers. Circulate to provide assistance and check for understanding.
  • Wrap Up (3 mins)
    Review the key steps of breaking apart numbers for addition. Ask students to share how this strategy helps them add more easily.

Interactive Exercises

  • Number Breakdown Game
    Write a two-digit number on the board. Have students come up and write the tens and ones that make up the number (e.g., 37 = 30 + 7). Then have a second number and ask for the sum of the tens places and the ones places.
  • Partner Add
    Have students work in pairs. One student writes a two-digit addition problem, and the other student solves it by breaking apart the numbers. Then they switch roles.

Discussion Questions

  • Why is it helpful to break apart numbers when we add?
  • Can you think of a time when breaking apart a number would make adding easier?
  • What is another strategy you can use to add two digit numbers?

Skills Developed

  • Place Value Recognition
  • Addition
  • Problem-Solving
  • Critical Thinking

Multiple Choice Questions

Question 1:

What does the 3 in 35 stand for?

Correct Answer: 3 tens

Question 2:

Which of these shows 28 broken apart into tens and ones?

Correct Answer: 20 + 8

Question 3:

If you break apart 42 into 40 + 2, what are you showing?

Correct Answer: The place value of each number

Question 4:

Which is the same as 56 + 23?

Correct Answer: (50 + 20) + (6 + 3)

Question 5:

What is 30 + 7?

Correct Answer: 37

Question 6:

What is 10 + 10?

Correct Answer: 20

Question 7:

If you break 67 into tens and ones, how many tens do you have?

Correct Answer: 6

Question 8:

If you break 94 into tens and ones, how many ones do you have?

Correct Answer: 4

Question 9:

Which sum helps you solve 21 + 12?

Correct Answer: 20 + 10

Question 10:

If you break apart 11 + 13 into tens and ones, what does that look like?

Correct Answer: 10 + 1 + 10 + 3

Fill in the Blank Questions

Question 1:

The number 62 has 6 _______ and 2 ones.

Correct Answer: tens

Question 2:

When we break apart 45 into 40 + 5, we are showing its _______ value.

Correct Answer: place

Question 3:

30 + 8 = _______

Correct Answer: 38

Question 4:

To add 21 + 15, we can add the tens: 20 + 10 = _______.

Correct Answer: 30

Question 5:

To add 21 + 15, we can add the ones: 1 + 5 = _______.

Correct Answer: 6

Question 6:

90 + 9 = _______

Correct Answer: 99

Question 7:

72 has _______ tens

Correct Answer: 7

Question 8:

The ones place of 34 has _______ ones.

Correct Answer: 4

Question 9:

14 + 11 = _______ + _______ + _______ + _______

Correct Answer: 10

Question 10:

14 + 11 = 10 + 4 + 10 + _______

Correct Answer: 1

Educational Standards

1.NBT.C.4:Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten. 1.NBT.B.2:Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases: CCSS.Math.Content.1.OA.A.1:Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.

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