Unit 1 · Topic 4

Decimal Operations

Overview

Line up the point to add or subtract; count places to multiply.

Topic 4 of 4~13 min
All units
Unit overview

The lesson

Read each section in order, work through every example on paper, then use the practice problems and quick check at the bottom.

Adding & subtracting decimals

Stack the numbers so the decimal points line up, then add or subtract like whole numbers. Fill empty spots with zeros so every column has a digit.

Worked example

4.5 − 2.75

  1. 1Line up the points: 4.50 − 2.75.
  2. 2Subtract column by column: 1.75.

Multiplying decimals

Ignore the decimal points and multiply like whole numbers. Then count the total number of decimal places in both factors and place the point that many spots from the right.

Worked example

0.6 × 0.4

  1. 16 × 4 = 24.
  2. 2Two decimal places total → 0.24.

Why this matters

Line up the point to add or subtract; count places to multiply.

These ideas show up on homework, quizzes, and the next unit in this grade. Getting comfortable here saves time later when the problems stack more steps together.

Common mistakes to avoid

Reversing the order named in the problem. Write the ratio in the same order the words give you.

Treating a part-to-part ratio like a part-to-whole fraction without checking what the whole is.

Key ideas from this lesson

  1. Adding & subtracting decimals
  2. Multiplying decimals

Video walkthroughs

Virtual Nerd

Multiplying Decimals

Multiply first, then place the decimal point.

Watch on YouTube
Virtual Nerd

Subtracting Decimals

Line up the decimal points, then subtract like whole numbers.

Watch on YouTube
Khan Academy

Adding Decimals

Line up decimal points and add multi-digit decimal numbers.

Watch on YouTube
Math Antics

Decimal Arithmetic

Add, subtract, multiply, and divide decimals by hand.

Watch on YouTube

Practice

For each problem: write your work in the box, type your answer, and check it. If you are stuck, reveal the solution one step at a time. Do not skip straight to the final answer.

Exercise 1

Try it yourself

What is 3.6 + 2.47?

Step-by-step solution

  1. 1Write as 3.60 + 2.47.
  2. 2Add hundredths, tenths, and ones: 6.07.

Exercise 2

Try it yourself

What is 8.2 − 5.75?

Step-by-step solution

  1. 1Line up decimals: 8.20 − 5.75.
  2. 2Subtract: 2.45.

Exercise 3

Try it yourself

What is 1.5 × 0.4?

Step-by-step solution

  1. 115 × 4 = 60.
  2. 2Two decimal places total → 0.60 = 0.6.

Exercise 4

Try it yourself

What is 0.25 × 3.2?

Step-by-step solution

  1. 125 × 32 = 800.
  2. 2Three decimal places total → 0.800 = 0.8.

Exercise 5

Try it yourself

You buy 3 notebooks at $2.35 each. How much do you pay in total?

Step-by-step solution

  1. 1Multiply: 3 × 2.35.
  2. 23 × 2.35 = 7.05.

Re-read the lesson section if you get stuck, then try again without peeking at the solution.

Math Worksheets 4 Kids

Decimal operations

Open resource

Quick check

Answer all questions. Retake the quiz until you feel confident before moving on.

Decimal Operations

Question 1 of 5

Medium

0.6 × 0.4 = ?

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