Decimal Addition: Calculate the Sum of $4.5 and $8.2

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

Lining up decimal points ensures you're adding the same place values: tenths with tenths, ones with ones, etc. Without this alignment, you'll get completely wrong answers!

Q: What if one decimal has more digits than the other?

That's okay! You can add invisible zeros to make them the same length. For example, treat 4.5 as 4.50 when adding to 8.23.

Q: How do I check if my decimal addition is correct?

Use estimation! Round each decimal to the nearest whole number, add them, and see if your answer is close. For $ 4.5 + 8.2 $, estimate: 5 + 8 = 13, so 12.7 makes sense!

Q: Do I need to put a dollar sign in my final answer?

Yes! Since this problem asks about money, always include the dollar sign ($) to show the units. Your final answer should be $12.7 or $12.70.

Q: Can I add decimals in my head without writing them down?

For simple problems like this, yes! Think: 4 + 8 = 12 for the whole parts, then 0.5 + 0.2 = 0.7 for the decimal parts. Combined: 12.7!

Decimal Addition with Real-World Applications

A father gives his son Nicolas $4.5$ dollars and his son Daniel $8.2$ dollars.

How much does he give to Nicolas and Daniel in total?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Solve

00:04 We will use long addition for calculation

00:11 Each time we'll add, calculate and substitute accordingly

00:24 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

A father gives his son Nicolas $4.5$ dollars and his son Daniel $8.2$ dollars.

How much does he give to Nicolas and Daniel in total?

Step-by-step solution

In order to determine how much money the father gave to Nicolas and Daniel, we'll add up the various amounts of money in the vertical format as follows:

$4.5\\+8.2$

We'll add from right to left as follows:

$12.7$

Final Answer

$\( 12.7$

Key Points to Remember

Essential concepts to master this topic

Rule: Align decimal points vertically to add correctly
Technique: Add column by column: 5 + 2 = 7, 4 + 8 = 12
Check: Estimate first: 4.5 ≈ 5, 8.2 ≈ 8, so 5 + 8 = 13 ≈ 12.7 ✓

Common Mistakes

Avoid these frequent errors

Adding decimals without aligning decimal points
Don't line up the rightmost digits instead of decimal points = 4.5 + 8.2 becomes 45 + 82 = 127! This treats decimals like whole numbers and gives wildly wrong answers. Always align the decimal points vertically first, then add column by column.

Practice Quiz

Test your knowledge with interactive questions

Which decimal number is greater?

FAQ

Everything you need to know about this question

Why do I need to line up the decimal points?

Lining up decimal points ensures you're adding the same place values: tenths with tenths, ones with ones, etc. Without this alignment, you'll get completely wrong answers!

What if one decimal has more digits than the other?

That's okay! You can add invisible zeros to make them the same length. For example, treat 4.5 as 4.50 when adding to 8.23.

How do I check if my decimal addition is correct?

Use estimation! Round each decimal to the nearest whole number, add them, and see if your answer is close. For $4.5 + 8.2$ , estimate: 5 + 8 = 13, so 12.7 makes sense!

Do I need to put a dollar sign in my final answer?

Yes! Since this problem asks about money, always include the dollar sign ( $) to show the units. Your final answer should be$ 12.7 or $12.70.

Can I add decimals in my head without writing them down?

For simple problems like this, yes! Think: 4 + 8 = 12 for the whole parts, then 0.5 + 0.2 = 0.7 for the decimal parts. Combined: 12.7!

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