Subtracting Tens: Fun with Numbers!

Math Grades 1st Grade 2:09 Video
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Lesson Description

Learn how to subtract tens using place value understanding. We'll use groups of tens to make subtraction easy and fun!

Video Resource

Subtract tens exercise | Addition and subtraction within 100 | Early Math | Khan Academy

Khan Academy

Duration: 2:09
Watch on YouTube

Key Concepts

  • Place value (tens and ones)
  • Subtraction as taking away
  • Relationship between addition and subtraction
  • Representing numbers as groups of tens

Learning Objectives

  • Students will be able to subtract multiples of 10 from multiples of 10 within the range of 10-90.
  • Students will be able to represent numbers as groups of tens.
  • Students will be able to relate subtraction to finding the missing addend.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students what they know about subtraction. Review the concept of 'taking away'. Introduce the idea that today we'll be subtracting groups of ten. Ask them to count by tens to 100.
  • Video Viewing (5 mins)
    Play the Khan Academy video "Subtract tens exercise | Addition and subtraction within 100 | Early Math | Khan Academy". Encourage students to pay attention to how the narrator uses 'tens' to explain the subtraction problems.
  • Guided Practice (10 mins)
    Work through a few example problems on the board, similar to those in the video. For example, write '70 - 20 = ?'. Guide students to understand that 70 is 7 tens and 20 is 2 tens. So, 7 tens - 2 tens = 5 tens, which is 50. Use manipulatives like connecting cubes grouped in tens to visually represent the problem.
  • Independent Practice (10 mins)
    Provide students with a worksheet containing subtraction problems involving multiples of 10 (e.g., 60 - 30, 80 - 10, 90 - 50). Have them solve the problems independently, using drawings or manipulatives if needed.
  • Wrap-up (5 mins)
    Review the answers to the independent practice problems. Ask students to explain how they solved the problems, emphasizing the use of 'tens'. Briefly introduce the concept of the relationship between addition and subtraction by asking questions like 'What number plus 30 equals 60?'

Interactive Exercises

  • Tens Tower Subtraction
    Provide students with connecting cubes. Have them build towers representing multiples of ten. Then, ask them to subtract by removing cubes from the tower. For example, build a tower of 60 cubes (6 tens). Then, take away 20 cubes (2 tens). How many cubes are left?
  • Number Line Hop
    Use a number line that counts by tens (10, 20, 30...). Start at a given number (e.g., 80) and have students 'hop back' by a certain number of tens (e.g., hop back 3 tens). Where do they land?

Discussion Questions

  • What does it mean when we say a number is a 'ten'?
  • How can knowing how to subtract small numbers (like 5-2) help us subtract tens (like 50-20)?
  • Can you think of a time when you might need to subtract tens in real life?

Skills Developed

  • Subtraction
  • Place value understanding
  • Problem-solving
  • Visual representation

Multiple Choice Questions

Question 1:

What is 40 - 10?

Correct Answer: 30

Question 2:

Which is the same as 7 tens?

Correct Answer: 70

Question 3:

What is 90 minus 60?

Correct Answer: 30

Question 4:

How many tens are in the number 50?

Correct Answer: 50

Question 5:

What is 80 - 40?

Correct Answer: 40

Question 6:

6 tens is the same as...

Correct Answer: 60

Question 7:

What is 30 - 20?

Correct Answer: 10

Question 8:

Which is more: 9 tens or 4 tens?

Correct Answer: 9 tens

Question 9:

What number plus 20 equals 50?

Correct Answer: 30

Question 10:

If you have 70 and take away 30, how much do you have?

Correct Answer: 40

Fill in the Blank Questions

Question 1:

60 is the same as ____ tens.

Correct Answer: 6

Question 2:

80 - 50 = ____

Correct Answer: 30

Question 3:

3 tens is the same as ____.

Correct Answer: 30

Question 4:

90 - ____ = 40

Correct Answer: 50

Question 5:

____ - 10 = 20

Correct Answer: 30

Question 6:

5 tens - 2 tens = ____ tens

Correct Answer: 3

Question 7:

70 - 40 = ____

Correct Answer: 30

Question 8:

____ is the same as 4 tens.

Correct Answer: 40

Question 9:

20 - 10 = ____

Correct Answer: 10

Question 10:

10 + ____ = 60 - 10

Correct Answer: 40

Educational Standards

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. 1.NBT.B.2.C:The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones). 1.OA.B.4:Understand subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8.

Teaching Materials

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