Decimal Operations: Adding, Subtracting, Multiplying, and Dividing!

Mathematics Grades 5th Grade 10:55 Video
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Lesson Description

Let's review how to add, subtract, multiply, and divide decimals! We'll learn how to line them up, use placeholder zeros, and estimate our answers to make sure they make sense.

Video Resource

Decimal Review | Add, Subtract, Multiply, and Divide Decimals

Math with Mr. J

Duration: 10:55
Watch on YouTube

Key Concepts

  • Decimal Place Value
  • Adding and Subtracting Decimals (Alignment)
  • Multiplying Decimals (Counting Decimal Places)
  • Dividing Decimals (Making the Divisor a Whole Number)

Learning Objectives

  • Students will be able to accurately add and subtract decimals by aligning decimal points and using placeholder zeros.
  • Students will be able to multiply decimals and correctly place the decimal point in the product by counting decimal places.
  • Students will be able to divide decimals by converting the divisor to a whole number and adjusting the dividend accordingly.

Educator Instructions

  • Introduction (5 mins)
    Begin by watching the 'Decimal Review' video by Math with Mr. J. Pay attention to the examples of addition, subtraction, multiplication, and division of decimals. Take notes on the key steps for each operation.
  • Addition and Subtraction of Decimals (10 mins)
    Focus on the importance of lining up the decimal points when adding and subtracting. Discuss why placeholder zeros are necessary and how they do not change the value of the number. Work through additional examples together as a class.
  • Multiplication of Decimals (10 mins)
    Explain that you don't need to line up the decimals for multiplication. Instead, multiply as if they are whole numbers and then count the total number of decimal places in the factors to determine the placement of the decimal point in the product. Provide more practice problems.
  • Division of Decimals (10 mins)
    Emphasize the rule that the divisor must be a whole number. Explain how to move the decimal point in both the divisor and the dividend. Work through several division problems together, making sure to bring the decimal point straight up into the quotient.
  • Estimation and Reasonableness (5 mins)
    Reinforce the concept of estimation to check the reasonableness of answers. Practice rounding the numbers in the original problems to whole numbers and performing the operations to estimate the solution. Compare the estimated solution with the calculated answer.

Interactive Exercises

  • Decimal Dice Game
    Students roll dice to create decimal numbers and then add, subtract, multiply or divide them. This provides hands-on practice with decimal operations.
  • Real-World Decimal Problems
    Present word problems that involve decimals in real-life scenarios such as buying items at a store, measuring ingredients for a recipe, or calculating distances. This helps students understand the practical application of decimal operations.

Discussion Questions

  • Why is it important to line up the decimal points when adding and subtracting decimals?
  • How does estimation help you check if your answer to a decimal problem is reasonable?
  • What do you do if the divisor is not a whole number when dividing decimals?

Skills Developed

  • Computational Fluency with Decimals
  • Problem-Solving
  • Estimation and Reasoning

Multiple Choice Questions

Question 1:

What is 12.5 + 3.75?

Correct Answer: 15.25

Question 2:

What is 25.8 - 11.2?

Correct Answer: 14.6

Question 3:

What is 4.2 x 3.0?

Correct Answer: 12.6

Question 4:

What is 16.4 รท 4?

Correct Answer: 4.1

Question 5:

When adding or subtracting decimals, what is the most important thing to do?

Correct Answer: Line up the decimal points

Question 6:

What do you need to do to the divisor before you divide decimals?

Correct Answer: Make it a whole number

Question 7:

What can you use to help decide if your answer is correct?

Correct Answer: estimation

Question 8:

What is 0.25 + 0.25?

Correct Answer: 0.50

Question 9:

How many digits behind the decimal point are in the answer to 2.5 x 2.5?

Correct Answer: 2

Question 10:

Which of the following is a equivalent decimal to 18.4?

Correct Answer: 18.40

Fill in the Blank Questions

Question 1:

Zeros to the _____ of a decimal do not change the value.

Correct Answer: right

Question 2:

When dividing decimals, the _____ needs to be a whole number.

Correct Answer: divisor

Question 3:

When multiplying decimals, you don't need to line up the _____.

Correct Answer: decimals

Question 4:

_____ is a way to see if your answer to a decimal problem makes sense.

Correct Answer: Estimation

Question 5:

In the number 34.6, the 6 is in the ______ place.

Correct Answer: tenths

Question 6:

When adding and subtracting you must line up the ______.

Correct Answer: decimals

Question 7:

Equivalent means ______.

Correct Answer: equal

Question 8:

2.5 x 10 is ______.

Correct Answer: 25

Question 9:

10 / 2.5 is ______.

Correct Answer: 4

Question 10:

In the number 13.76, the 6 is in the ______ place.

Correct Answer: hundredths

Educational Standards

5.N.3.3:Add and subtract fractions with like and unlike denominators, mixed numbers, and decimals, involving money, measurement, geometry, and data. Use various models and efficient strategies, including but not limited to standard algorithms. 5.N.2.2:Divide multi-digit numbers, by one- and two-digit divisors, based on knowledge of place value, including but not limited to standard algorithms. 5.N.3.1:Estimate sums and differences of fractions with like and unlike denominators, mixed numbers, and decimals to assess the reasonableness of the results.

Teaching Materials

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