Taking Away Tens: Understanding Place Value

Math Grades 1st Grade 2:36 Video
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Lesson Description

Let's learn how to subtract tens from two-digit numbers using place value! We'll use blocks and numbers to help us understand what's happening when we take away groups of ten.

Video Resource

Understanding place value when subtracting tens | Early Math | Khan Academy

Khan Academy

Duration: 2:36
Watch on YouTube

Key Concepts

  • Place Value (Tens and Ones)
  • Subtracting Tens
  • Representing Numbers with Blocks

Learning Objectives

  • Students will be able to identify the tens and ones digits in a two-digit number.
  • Students will be able to subtract multiples of 10 from a two-digit number using place value understanding.
  • Students will be able to represent subtraction of tens using visual aids (like blocks).

Educator Instructions

  • Introduction (5 mins)
    Begin by reviewing place value. Ask students: 'What does the number 32 mean? How many tens and how many ones?' Use base ten blocks to visually represent numbers like 32, 45, etc.
  • Video Viewing (7 mins)
    Play the Khan Academy video 'Understanding place value when subtracting tens | Early Math | Khan Academy'. Pause at key points to ask clarifying questions and reinforce concepts.
  • Guided Practice (10 mins)
    Work through examples similar to the video on the whiteboard. For example: 'We have 57 blocks. If we take away 20 blocks, how many are left?' Guide students to understand that they are subtracting 2 tens from 5 tens.
  • Independent Practice (10 mins)
    Provide students with worksheets or base ten blocks to solve subtraction problems involving tens. Examples: 43 - 10, 68 - 30, 91 - 50. Encourage them to draw pictures if needed.
  • Wrap-up (3 mins)
    Review the key concepts. Ask students to explain in their own words how subtracting tens works. Quick check: 'What is 76 minus 40?'

Interactive Exercises

  • Base Ten Block Subtraction
    Give each student a set of base ten blocks. Call out a subtraction problem (e.g., 63 - 20). Have students represent the first number with blocks, then physically remove the correct number of tens blocks to find the answer.
  • Number Line Hop
    Use a number line (either a large one on the floor or individual ones for each student). Start at a two-digit number and hop back by tens to solve subtraction problems. For example, start at 54 and hop back 3 tens to solve 54-30.

Discussion Questions

  • What happens to the ones when we only subtract tens?
  • How is subtracting tens similar to subtracting ones?
  • Can you think of a time when you might need to subtract tens in real life?

Skills Developed

  • Place Value Understanding
  • Subtraction Skills
  • Problem-Solving

Multiple Choice Questions

Question 1:

What does the 2 in 25 mean?

Correct Answer: 2 tens

Question 2:

If you have 43 blocks and take away 10, how many are left?

Correct Answer: 33

Question 3:

Which number has 3 tens?

Correct Answer: 35

Question 4:

60 - 20 = ?

Correct Answer: 40

Question 5:

What is the same as 5 tens?

Correct Answer: 50

Question 6:

If you start with 88 and take away 40, what do you have left?

Correct Answer: 48

Question 7:

Which group of blocks shows 7 tens?

Correct Answer: |||||||

Question 8:

Which is the correct way to show 90 - 30?

Correct Answer: 90 - 30

Question 9:

You have 5 tens and your friend takes 2 tens. How many tens do you have now?

Correct Answer: 3

Question 10:

What is ten less than 62?

Correct Answer: 52

Fill in the Blank Questions

Question 1:

The number 34 has 3 ______ and 4 ones.

Correct Answer: tens

Question 2:

50 - 10 = ______

Correct Answer: 40

Question 3:

Taking away tens changes the ______ place.

Correct Answer: tens

Question 4:

7 tens is the same as the number ______.

Correct Answer: 70

Question 5:

82 - ______ = 52

Correct Answer: 30

Question 6:

66 minus 40 is ____

Correct Answer: 26

Question 7:

If you have 90 and take away all the tens, you have ______ left.

Correct Answer: 0

Question 8:

Ten more than 45 is ______.

Correct Answer: 55

Question 9:

9 tens - 2 tens = _____ tens

Correct Answer: 7

Question 10:

The number before 30 is _____

Correct Answer: 29

Educational Standards

1.NBT.C.5:Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used. 1.NBT.B.2:Understand that the two digits of a two-digit number represent amounts of tens and ones. 1.NBT.C.6:Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), 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.

Teaching Materials

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