Making Addition Easier: Rounding Numbers to Add

Mathematics Grades 4th Grade 3:57 Video
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Lesson Description

Learn how to make addition problems easier by rounding numbers to multiples of 10 and 100. This lesson uses strategies like taking from one number and giving to another to create 'rounder' numbers that are simpler to add mentally.

Video Resource

Addition using groups of 10 and 100 | 2nd grade | Khan Academy

Khan Academy

Duration: 3:57
Watch on YouTube

Key Concepts

  • Place Value
  • Rounding to Nearest 10 and 100
  • Commutative Property of Addition

Learning Objectives

  • Students will be able to rewrite addition problems by adjusting addends to create multiples of 10 or 100.
  • Students will be able to mentally add numbers by using the rounding strategy demonstrated in the video.
  • Students will be able to explain why this strategy works based on the properties of addition.

Educator Instructions

  • Introduction (5 mins)
    Begin by reviewing place value (ones, tens, hundreds). Ask students to share strategies they already use for adding numbers, especially larger numbers. Introduce the concept of 'friendly numbers' (multiples of 10 and 100) and why they are easier to work with.
  • Video Viewing (7 mins)
    Watch the Khan Academy video 'Addition using groups of 10 and 100'. Encourage students to take notes on the examples presented in the video.
  • Guided Practice (10 mins)
    Work through a few examples on the board, similar to those in the video. Emphasize the step-by-step process: identifying a number to 'round', determining how much to add/subtract, and adjusting the other number accordingly. For example: 48 + 23 becomes 50 + 21. Explain why the total remains the same.
  • Independent Practice (10 mins)
    Provide students with a worksheet of addition problems. Instruct them to use the rounding strategy to rewrite and solve each problem. Encourage them to show their work.
  • Wrap-up & Discussion (3 mins)
    Review the main points of the lesson. Ask students to share their experiences using the rounding strategy and discuss when it might be most useful.

Interactive Exercises

  • Number Line Rounding
    Use a number line to visually demonstrate how taking away from one number and adding to another doesn't change the overall distance (sum). Start with a simple example, like 7 + 5, and move units between the numbers to create 10 + 2.
  • Partner Practice
    Have students pair up and create their own addition problems. They should then trade problems and solve them using the rounding strategy. Partners can check each other's work.

Discussion Questions

  • Why are multiples of 10 and 100 easier to add mentally?
  • Can you think of other situations where making numbers 'rounder' can help you solve problems?
  • Does it matter which number you choose to round in an addition problem? Why or why not?

Skills Developed

  • Mental Math
  • Problem-Solving
  • Number Sense

Multiple Choice Questions

Question 1:

What does it mean to 'round' a number?

Correct Answer: To change a number to a nearby easier number

Question 2:

Which number is closest to 30 when rounding to the nearest ten?

Correct Answer: 31

Question 3:

If you add 3 to one number in an addition problem, what must you do to the other number to keep the answer the same?

Correct Answer: Subtract 3

Question 4:

Why do we round numbers when adding?

Correct Answer: To make the problem easier to solve in our heads

Question 5:

What number can you add to 67 to make it 70?

Correct Answer: 3

Question 6:

Which of these is the easiest to add?

Correct Answer: 30 + 10

Question 7:

What is 254 rounded to the nearest hundred?

Correct Answer: 300

Question 8:

To make 58 a 'rounder' number, we can add 2. Which 'rounder' number would that be?

Correct Answer: 60

Question 9:

What is 38 + 42 if you made 38 into 40?

Correct Answer: 80

Question 10:

Which is the 'rounder' number?

Correct Answer: 70

Fill in the Blank Questions

Question 1:

Numbers that end in zero are called ____________ numbers.

Correct Answer: round

Question 2:

When you round, you change a number to a number that is ____________ to add.

Correct Answer: easier

Question 3:

If you add to one number, you must ____________ from the other number.

Correct Answer: subtract

Question 4:

45 + 25 is the same as 50 + _________.

Correct Answer: 20

Question 5:

Adding or subtracting the same amount doesn't change the ____________ of the addition problem.

Correct Answer: value

Question 6:

A 'rounder' number is often a multiple of _____ or 100.

Correct Answer: 10

Question 7:

Using place value helps you ____________ numbers to solve addition problems.

Correct Answer: rewrite

Question 8:

16 + 34 can be 'rounded' to _______ + 30

Correct Answer: 20

Question 9:

68 + 12 can be made easier by changing the problem to 70 + ________

Correct Answer: 10

Question 10:

If a number ends with a 5, 6, 7, 8, or 9, you round ____________.

Correct Answer: up

Educational Standards

4.N.1.2:Use place value to describe whole numbers between 1,000 and 1,000,000 in terms of millions, hundred thousands, ten thousands, thousands, hundreds, tens, and ones with written, standard, and expanded forms. 4.N.2.4:Apply and analyze models to solve multi-step problems requiring the use of addition, subtraction, and multiplication of multi-digit whole numbers. Use various strategies, including the relationship between operations, the use of appropriate technology, and the context of the problem to assess the reasonableness of results. 4.N.1.3:Applying knowledge of place value, use mental strategies (no written computations) to multiply or divide a number by 10, 100, and 1,000.

Teaching Materials

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