Subtracting Two-Digit Numbers Without Regrouping: Tens and Ones

Math Grades 1st Grade 2:36 Video
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Lesson Description

Learn how to subtract two-digit numbers by understanding tens and ones places, without needing to regroup.

Video Resource

Subtracting two digit numbers without regrouping | Early Math | Khan Academy

Khan Academy

Duration: 2:36
Watch on YouTube

Key Concepts

  • Place Value (Tens and Ones)
  • Subtraction as taking away
  • Subtracting ones from ones and tens from tens

Learning Objectives

  • Students will be able to identify the tens and ones place in a two-digit number.
  • Students will be able to subtract a two-digit number from another two-digit number without regrouping.
  • Students will be able to explain their subtraction process using the concept of tens and ones.

Educator Instructions

  • Introduction (5 mins)
    Begin by reviewing the concept of place value (tens and ones) with the students. Use visual aids like base-ten blocks if available. Ask students to identify the tens and ones in various two-digit numbers (e.g., 37, 52, 81).
  • Video Viewing (5 mins)
    Play the Khan Academy video: 'Subtracting two digit numbers without regrouping'. Encourage students to pay attention to how the narrator explains the process using tens and ones.
  • Guided Practice (10 mins)
    Work through a few subtraction problems on the board, mirroring the method shown in the video. For example, 48 - 12. Clearly demonstrate subtracting the ones (8-2) and then the tens (4-1). Emphasize the importance of keeping the ones and tens separate.
  • Independent Practice (10 mins)
    Provide students with a worksheet containing subtraction problems without regrouping. Have them solve the problems independently, showing their work by writing the subtraction of ones and tens separately.
  • Wrap-up (5 mins)
    Review the answers to the worksheet. Ask students to explain how they solved a particular problem, reinforcing the concept of subtracting tens and ones separately.

Interactive Exercises

  • Base-Ten Block Subtraction
    Provide students with base-ten blocks. Give them a subtraction problem (e.g., 54 - 21). Have them represent the larger number with the blocks and then physically remove the blocks representing the smaller number. Count the remaining blocks to find the answer.
  • Number Line Subtraction
    Use a number line to visualize subtraction. For the problem 35-13, students can start at 35 and jump back 13 spaces, first jump back 3 spaces to 32 (subtracting the ones), then jump back 10 spaces to 22 (subtracting the tens).

Discussion Questions

  • Why is it important to subtract the ones first and then the tens?
  • Can you think of a time when you would need to subtract two-digit numbers in real life?

Skills Developed

  • Understanding Place Value
  • Subtraction Skills
  • Problem-Solving

Multiple Choice Questions

Question 1:

What number is in the ones place in 42?

Correct Answer: 2

Question 2:

What number is in the tens place in 65?

Correct Answer: 6

Question 3:

What is 5 - 2?

Correct Answer: 3

Question 4:

What is 7 - 3?

Correct Answer: 4

Question 5:

What is 8 - 4?

Correct Answer: 4

Question 6:

What is 9 - 5?

Correct Answer: 4

Question 7:

Solve: 36 - 12 = ?

Correct Answer: 24

Question 8:

Solve: 58 - 23 = ?

Correct Answer: 35

Question 9:

Solve: 99 - 33 = ?

Correct Answer: 66

Question 10:

Solve: 45 - 15 = ?

Correct Answer: 30

Fill in the Blank Questions

Question 1:

In the number 72, the 7 is in the _______ place.

Correct Answer: tens

Question 2:

In the number 39, the 9 is in the _______ place.

Correct Answer: ones

Question 3:

68 - 24 = ____

Correct Answer: 44

Question 4:

47 - 13 = ____

Correct Answer: 34

Question 5:

86 - 32 = ____

Correct Answer: 54

Question 6:

25 - 11 = ____

Correct Answer: 14

Question 7:

54 - 21 = ____

Correct Answer: 33

Question 8:

If you have 3 tens and take away 1 ten, you have ____ tens left.

Correct Answer: 2

Question 9:

If you have 8 ones and take away 3 ones, you have ____ ones left.

Correct Answer: 5

Question 10:

78 - ____ = 48. What is the missing number?

Correct Answer: 30

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.

Teaching Materials

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