Solve for Missing Addend: 0.3 + ? = 0.8

Q: Why do I subtract 0.3 from 0.8 instead of adding them?

Think of it like this: if you have 0.3 + ? = 0.8, you're asking 'what do I add to 0.3 to get 0.8?' To find that missing piece, you take away what you already have (0.3) from the total (0.8).

Q: How do I line up the decimal points when subtracting?

Write the numbers in a column with decimal points directly under each other: 0.8- 0.3-----This keeps the tenths place aligned with tenths place!

Q: What if I get confused about which number to subtract from which?

Remember the pattern: missing addend = sum - known addend. So ? = 0.8 - 0.3. The sum is always the larger number you subtract from.

Q: Can I check my answer a different way?

Yes! Try counting up from 0.3 to 0.8: 0.3 → 0.4 → 0.5 → 0.6 → 0.7 → 0.8. You count 5 tenths, which is 0.5!

Decimal Addition with Missing Addends

Fill in the missing value (?):

$\text{0.3+?=0}.8$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:05 Let's choose the correct answer together!

00:08 First, we'll write down each option and check them one by one.

00:15 We'll do calculations step-by-step. Ready?

00:19 Let's calculate and write it down clearly.

00:37 Great! The first option fits. Now, let's try the second option.

00:46 We'll use the same method to check this one.

00:57 Calculate carefully and let's write it down.

01:08 Oops, the second option doesn't fit. Let's move to the third.

01:17 Again, use the same method to check the third option.

01:25 Calculate and write it down thoroughly.

01:40 The third option fits doesn't fit. Let's try the fourth.

01:50 Once more, use the same method to check the fourth option.

01:58 Let's calculate accurately and note it down.

02:08 Looks like the fourth option doesn't fit.

02:13 And that's the solution to our question!

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Fill in the missing value (?):

$\text{0.3+?=0}.8$

Step-by-step solution

Let's work through the solution by performing the necessary calculation:

Step 1: Identify the known values:
The equation provided is $0.3 + ? = 0.8$ .
Step 2: Use the subtraction operation to solve for the missing number, ?:
We need to subtract $0.3$ from $0.8$ .

Calculation:
$\text{?} = 0.8 - 0.3$

We perform the subtraction as follows:

Write both numbers with the decimal points aligned:
$0.8$
$- 0.3$
Perform the subtraction:
$0.8 - 0.3 = 0.5$

Thus, the missing number is $\textbf{0.5}$ .

Therefore, the correct answer is $\textbf{0.5}$ .

Final Answer

0.5

Key Points to Remember

Essential concepts to master this topic

Rule: Use subtraction to find the missing addend in addition equations
Technique: Calculate ? = 0.8 - 0.3 by aligning decimal points
Check: Verify that 0.3 + 0.5 = 0.8 to confirm your answer ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting to solve
Don't add 0.3 + 0.8 = 1.1 to find the missing number! This gives you the wrong operation and an impossible result. Always subtract the known addend from the sum to find the missing addend.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I subtract 0.3 from 0.8 instead of adding them?

Think of it like this: if you have 0.3 + ? = 0.8, you're asking 'what do I add to 0.3 to get 0.8?' To find that missing piece, you take away what you already have (0.3) from the total (0.8).

How do I line up the decimal points when subtracting?

Write the numbers in a column with decimal points directly under each other:

0.8
- 0.3
-----

This keeps the tenths place aligned with tenths place!

What if I get confused about which number to subtract from which?

Remember the pattern: missing addend = sum - known addend. So ? = 0.8 - 0.3. The sum is always the larger number you subtract from.

Can I check my answer a different way?

Yes! Try counting up from 0.3 to 0.8: 0.3 → 0.4 → 0.5 → 0.6 → 0.7 → 0.8. You count 5 tenths, which is 0.5!

Why is 0.5 the right answer and not 0.6?

Let's check both: 0.3 + 0.5 = 0.8 ✓ (correct!) but 0.3 + 0.6 = 0.9 ✗ (too big!). Only 0.5 makes the equation balance.

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