Solve Decimal Addition: 123.421 + 615.3 Step by Step

Decimal Addition with Different Place Values

Solve the following exercise:

123.421+615.3

❤️ Continue Your Math Journey!

We have hundreds of course questions with personalized recommendations + Account 100% premium

Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:08 Let's solve the problem together.
00:11 First, place zero in the right spots.
00:14 Then, we will add carefully, step by step. Remember to place each number correctly.
00:27 And there you have it, that's the solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the following exercise:

123.421+615.3

2

Step-by-step solution

To avoid confusion in solving the exercise, we will first add two zeros to the number 615.3 as follows:

123.421+615.300 123.421\\+615.300\\

Now let's solve the exercise in order:

Let's connect the thousandths after the decimal point:

1+0=1 1+0=1

Let's connect the hundredths after the decimal point:

2+0=2 2+0=2

Let's connect the tenths after the decimal point:

4+3=7 4+3=7

Finally, let's connect the whole numbers before the decimal point accordingly:

3+5=8 3+5=8

2+1=3 2+1=3

1+6=7 1+6=7

And we obtain the following:

123.421+615.300738.721 123.421\\+615.300\\738.721

3

Final Answer

738.721

Key Points to Remember

Essential concepts to master this topic
  • Alignment Rule: Line up decimal points vertically before adding
  • Technique: Add zeros to match decimal places: 615.3 becomes 615.300
  • Check: Count decimal places: 3 places in answer matches longest addend ✓

Common Mistakes

Avoid these frequent errors
  • Adding without aligning decimal points
    Don't add 123.421 + 615.3 by ignoring decimal alignment = wrong place values! This treats 615.3 as if it's 6153, giving massive errors. Always align decimal points vertically and add zeros to match decimal places.

Practice Quiz

Test your knowledge with interactive questions

Choose the correct writing form:

FAQ

Everything you need to know about this question

Why do I need to add zeros to 615.3?

+

Adding zeros like 615.300 615.300 helps you see each place value clearly! It doesn't change the number's value, but makes column addition much easier and prevents mistakes.

What if the decimal numbers have different lengths?

+

No problem! Always add zeros to make them the same length. For example: 123.421 has 3 decimal places, so 615.3 becomes 615.300.

Do I need to line up the decimal points?

+

Yes! Always line up decimal points vertically. Think of it like adding regular numbers - ones go under ones, tens under tens, and so on.

How do I know where the decimal point goes in my answer?

+

The decimal point in your answer goes directly below the decimal points in the numbers you're adding. It stays in the same column!

What if I get confused about which digits to add?

+

Add column by column from right to left:

  • Thousandths: 1 + 0 = 1
  • Hundredths: 2 + 0 = 2
  • Tenths: 4 + 3 = 7
  • Then add the whole numbers normally!

Can I check my answer somehow?

+

Yes! Try adding in reverse order: 615.300+123.421 615.300 + 123.421 . You should get the same answer: 738.721!

🌟 Unlock Your Math Potential

Get unlimited access to all 18 Decimal Fractions - Advanced questions, detailed video solutions, and personalized progress tracking.

📹

Unlimited Video Solutions

Step-by-step explanations for every problem

📊

Progress Analytics

Track your mastery across all topics

🚫

Ad-Free Learning

Focus on math without distractions

No credit card required • Cancel anytime

More Questions

Click on any question to see the complete solution with step-by-step explanations