Calculate the Sum: 20.4 + 10.4 Decimal Addition Problem

Q: Why do I need to line up the decimal points?

Aligning decimal points ensures you're adding like place values: tenths with tenths, ones with ones. Without proper alignment, you'll get the wrong answer!

Q: What if the decimal numbers have different numbers of digits?

No problem! You can add zeros as placeholders to make them the same length. For example, 20.4 + 10.40 works the same way.

Q: How do I know where to put the decimal point in my answer?

The decimal point in your answer goes in the same column as the decimal points in the numbers you're adding. It lines up perfectly!

Q: Can I add decimals without writing them in columns?

While possible with practice, column format prevents mistakes and makes the process clearer. It's especially helpful with longer decimal numbers!

Q: What if my answer doesn't look right?

Double-check by estimating: 20 + 10 = 30, so your answer should be close to 30. Since 30.8 is close to 30, it makes sense!

Decimal Addition with Like Place Values

$20.4+10.4=$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:04 Let's solve it together!

00:07 First, we will use long addition to calculate.

00:13 Remember to place the decimal point correctly.

00:16 Start by adding the smallest digits.

00:19 Continue adding and remember each step counts, so calculate carefully.

00:30 And there you have it, the answer is complete!

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

$20.4+10.4=$

Step-by-step solution

To solve this problem, we'll add the decimal numbers $20.4$ and $10.4$ by aligning the decimal points:

Step 1: Write the numbers in a column aligning their decimal points:

$\begin{array}{r} 20.4 \\ +10.4 \\ \hline \end{array}$

Step 2: Add the numbers starting from the right. First, $4 + 4 = 8$ .
Next, add the digits to the left of the decimal point: $0 + 0 = 0$ .
Finally, add the leftmost digits: $2 + 1 = 3$ .

Combining these, the result is $30.8$ .

Thus, the solution to the problem is $\mathbf{30.8}$ .

Final Answer

30.8

Key Points to Remember

Essential concepts to master this topic

Alignment: Line up decimal points vertically before adding
Technique: Add column by column: 4 + 4 = 8 tenths
Check: Verify decimal point placement: 30.8 has 8 tenths ✓

Common Mistakes

Avoid these frequent errors

Not aligning decimal points properly
Don't line up the rightmost digits ignoring decimal points = 30.4 instead of 30.8! This misplaces the decimal point and gives the wrong answer. Always align decimal points first, then add column by column.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I need to line up the decimal points?

Aligning decimal points ensures you're adding like place values: tenths with tenths, ones with ones. Without proper alignment, you'll get the wrong answer!

What if the decimal numbers have different numbers of digits?

No problem! You can add zeros as placeholders to make them the same length. For example, 20.4 + 10.40 works the same way.

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

The decimal point in your answer goes in the same column as the decimal points in the numbers you're adding. It lines up perfectly!

Can I add decimals without writing them in columns?

While possible with practice, column format prevents mistakes and makes the process clearer. It's especially helpful with longer decimal numbers!

What if my answer doesn't look right?

Double-check by estimating: 20 + 10 = 30, so your answer should be close to 30. Since 30.8 is close to 30, it makes sense!

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