Solve Decimal Addition: 0.8 + 0.4 Step-by-Step

Q: Why can't I just add 8 + 4 = 12 and write 0.12?

Because place value matters! When 8 + 4 = 12 in the tenths place, the 2 stays in tenths and the 1 moves to ones place. Writing 0.12 means you have 1 hundredth and 2 thousandths, which is much smaller than the correct answer.

Q: What does it mean to 'carry over' in decimal addition?

Carrying over means moving the extra digit to the next place value. When tenths place gives you 12, write down 2 and carry the 1 to the ones place, just like in whole number addition.

Q: How do I know when to carry over?

Carry over whenever the sum in any place value is 10 or greater. The digit in the tens position moves left, and the units digit stays in the current place.

Q: Can I check my answer using a different method?

Yes! Convert to fractions: $ 0.8 = \frac{8}{10} $ and $ 0.4 = \frac{4}{10} $. Adding gives $ \frac{12}{10} = 1.2 $.

Q: What if I forget to align the decimal points?

You'll get the wrong answer! Always line up decimal points vertically before adding. This ensures you're adding tenths to tenths, hundredths to hundredths, and so on.

Decimal Addition with Carrying Values

$0.8+0.4=$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Solve

00:03 Let's use long addition for calculation

00:08 Place the decimal point in the appropriate position

00:12 Let's start by adding the smallest appropriate digits

00:18 Place the units and remember to carry 1 up

00:28 Add 1 to this calculation, and place it

00:36 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

$0.8+0.4=$

Step-by-step solution

To solve this problem, we'll perform these steps:

Step 1: Align the numbers by their decimal points:
$0.8$
$+0.4$
Step 2: Add each corresponding position from right to left:

Adding the tenths place, we have $8 + 4 = 12$ . Write down the $2$ and carry over the $1$ to the ones place.

Add the ones place, which includes the carried-over $1$ :
$0 + 0 + 1 = 1$ .

Combining this, the sum of $0.8$ and $0.4$ is $1.2$ .

Therefore, the solution to the problem is $1.2$ . This corresponds to choice 2.

Final Answer

1.2

Key Points to Remember

Essential concepts to master this topic

Alignment: Line up decimal points to match place values correctly
Technique: Add tenths place: 8 + 4 = 12, write 2 and carry 1
Check: Verify by converting to fractions: 8/10 + 4/10 = 12/10 = 1.2 ✓

Common Mistakes

Avoid these frequent errors

Not carrying over when digits sum exceeds 9
Don't just write down 12 in the tenths place = 0.12! This ignores place value and gives completely wrong results. Always carry over the tens digit to the next higher place value when the sum is 10 or greater.

Practice Quiz

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FAQ

Everything you need to know about this question

Why can't I just add 8 + 4 = 12 and write 0.12?

Because place value matters! When 8 + 4 = 12 in the tenths place, the 2 stays in tenths and the 1 moves to ones place. Writing 0.12 means you have 1 hundredth and 2 thousandths, which is much smaller than the correct answer.

What does it mean to 'carry over' in decimal addition?

Carrying over means moving the extra digit to the next place value. When tenths place gives you 12, write down 2 and carry the 1 to the ones place, just like in whole number addition.

How do I know when to carry over?

Carry over whenever the sum in any place value is 10 or greater. The digit in the tens position moves left, and the units digit stays in the current place.

Can I check my answer using a different method?

Yes! Convert to fractions: $0.8 = \frac{8}{10}$ and $0.4 = \frac{4}{10}$ . Adding gives $\frac{12}{10} = 1.2$ .

What if I forget to align the decimal points?

You'll get the wrong answer! Always line up decimal points vertically before adding. This ensures you're adding tenths to tenths, hundredths to hundredths, and so on.

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