Adding Numbers Like a Detective: Finding the Easiest Path!

Math Grades 1st Grade 3:15 Video
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Lesson Description

Learn how to add two numbers by changing them into easier ones! We'll use fun strategies to make adding a piece of cake.

Video Resource

Strategies for adding 2-digit numbers | 2nd grade | Khan Academy

Khan Academy

Duration: 3:15
Watch on YouTube

Key Concepts

  • Addition Strategies
  • Making Tens
  • Place Value

Learning Objectives

  • Students will be able to identify different strategies for adding two numbers.
  • Students will be able to apply these strategies to simplify addition problems.
  • Students will be able to explain why these strategies work.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students: 'What's your favorite way to add numbers?'. Explain that sometimes, changing the numbers a little can make adding easier, like solving a puzzle!
  • Watch the Video (7 mins)
    Play the Khan Academy video 'Strategies for adding 2-digit numbers | 2nd grade | Khan Academy'. Ask students to pay attention to the different ways Sal adds numbers.
  • Discuss the Strategies (8 mins)
    After the video, discuss the strategies Sal used. Emphasize how he changed the numbers to make them easier to add, such as by 'making tens'.
  • Practice Problems (10 mins)
    Work through a few example problems together on the board. For example: 28 + 9. Guide students to think: 'What if we made 28 into 27 and 9 into 10?'.
  • Independent Practice (10 mins)
    Give students a worksheet with similar problems to solve on their own. Encourage them to try different strategies and see which works best for them.

Interactive Exercises

  • Number Swap Game
    Write addition problems on the board. Have students take turns suggesting how to 'swap' numbers to make the problem easier. For example: 19 + 6. A student could suggest changing it to 20 + 5.

Discussion Questions

  • Why is it helpful to change the numbers when we add?
  • Can you think of a time when changing the numbers wouldn't help?

Skills Developed

  • Addition fluency
  • Problem-solving
  • Number sense

Multiple Choice Questions

Question 1:

Which problem is the SAME as 36 + 8?

Correct Answer: 35 + 9

Question 2:

What is one way to make 17 + 3 easier?

Correct Answer: Make 17 into 20

Question 3:

Which of these equals 50?

Correct Answer: 30 + 20

Question 4:

Which number do we add to 32 to get 42?

Correct Answer: 20

Question 5:

Which is NOT a good strategy for adding?

Correct Answer: Adding all the numbers twice

Question 6:

To make 29 + 5 easier, what could you change 29 to?

Correct Answer: 30

Question 7:

If you take 2 away from one number, what should you do to the other number?

Correct Answer: Add 2

Question 8:

Which problem is the SAME as 45 + 5?

Correct Answer: 50 + 0

Question 9:

What does it mean to 'make a ten'?

Correct Answer: To change a number so it ends in 0

Question 10:

If you see 8 + 2 + 5, what should you add first?

Correct Answer: 8 + 2

Fill in the Blank Questions

Question 1:

Changing numbers slightly can make adding problems _________.

Correct Answer: easier

Question 2:

Making a ____ is a good way to add.

Correct Answer: ten

Question 3:

If you add to one number, you can _______ from the other number to keep it the same.

Correct Answer: subtract

Question 4:

40 + 10 = _______

Correct Answer: 50

Question 5:

When adding 27 + 3, you can change 27 to _____ to make it easier.

Correct Answer: 30

Question 6:

Addition is like a ________, sometimes you have to find the easiest way.

Correct Answer: puzzle

Question 7:

If you change 18 + 2 to 20 + 0, the answer is still _______.

Correct Answer: 20

Question 8:

15 + 5 is the same as ____ + 0.

Correct Answer: 20

Question 9:

Breaking a number apart to add is called ______.

Correct Answer: decomposing

Question 10:

Adding numbers is fun and can be ________!.

Correct Answer: easy

Educational Standards

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. 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.OA.B.3:Apply properties of operations as strategies to add and subtract. (Students need not use formal terms for these properties.) Examples: If 8 + 3 = 11 is known, then 3 + 8 = 11 is also known. (Commutative property of addition.) To add 2 + 6 + 4, the second two numbers can be added to make a ten, so 2 + 6 + 4 = 2 + 10 = 12. (Associative property of addition.)

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