Solve for the Missing Addend: 0.4 + ? = 0.9

Q: Why do I subtract instead of add to find the missing number?

Think of it like this: if you have 0.9 total and already used 0.4, you need to find what's left! Subtraction tells you the remaining amount: $ 0.9 - 0.4 = 0.5 $.

Q: How do I line up decimal numbers when subtracting?

Always line up the decimal points vertically! Write 0.9 above 0.4 with decimals aligned, then subtract normally: the answer is 0.5.

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

Remember: subtract the part from the whole! The sum (0.9) is the whole, and the known addend (0.4) is the part you already have.

Q: Can I solve this problem a different way?

Yes! You can also count up from 0.4 to 0.9. What do you add to 0.4 to reach 0.9? The answer is still 0.5!

Q: How do I check if my answer is correct?

Always substitute your answer back into the original equation. Does $ 0.4 + 0.5 = 0.9 $? Yes! So 0.5 is correct.

Missing Addend Problems with Decimal Numbers

Fill in the missing value (?):

$0.4+?=0.9$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:05 First, choose the correct answer.

00:09 Let's write down each option and check them one by one.

00:14 We'll use vertical addition for our calculations. Ready?

00:26 Let's calculate and write down the result.

00:34 The first option doesn't match. Let's move on to the second.

00:39 We'll try the same method again. Let's check it.

00:55 Calculate and write down the outcome.

01:08 This time, the second option works! Now, let's check the third.

01:16 Using the same method, let's analyze it.

01:25 Calculate and jot down the result.

01:37 The third option also fits. Let's look at the fourth.

01:46 Again, we'll use the same approach to check.

01:57 Let's go ahead and calculate the answer.

02:11 The fourth option doesn't match.

02:17 And there you have it, we've found the solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Fill in the missing value (?):

$0.4+?=0.9$

Step-by-step solution

To solve the problem of finding the missing value $?$ in the equation $0.4 + ? = 0.9$ , we'll perform the following steps:

Step 1: Identify what is given and what is missing in the equation.
Step 2: Use subtraction to isolate the missing value.
Step 3: Execute the subtraction and find the missing value.

Now, let's proceed through these steps in detail:

Step 1: The equation given is $0.4 + ? = 0.9$ . Here, the goal is to identify the number, represented by $?$ , which when added to $0.4$ equals $0.9$ .

Step 2: To find $?$ , we need to isolate it. We can do this by subtracting $0.4$ from both sides of the equation:

$? = 0.9 - 0.4$

Step 3: Calculate the result of the subtraction:

$? = 0.9 - 0.4 = 0.5$

Therefore, the missing value $?$ that satisfies the equation $0.4 + ? = 0.9$ is $0.5$ .

Let's confirm this with the multiple choice provided: the correct answer is choice :

0.5

Final Answer

0.5

Key Points to Remember

Essential concepts to master this topic

Rule: To find missing addend, subtract known addend from sum
Technique: Rearrange $0.4 + ? = 0.9$ to $? = 0.9 - 0.4$
Check: Substitute back: $0.4 + 0.5 = 0.9$ ✓

Common Mistakes

Avoid these frequent errors

Confusing which operation to use
Don't add the known values together like 0.4 + 0.9 = 1.3! This gives a wrong answer because you're adding instead of finding the difference. Always subtract the known addend from the total: ? = 0.9 - 0.4.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I subtract instead of add to find the missing number?

Think of it like this: if you have 0.9 total and already used 0.4, you need to find what's left! Subtraction tells you the remaining amount: $0.9 - 0.4 = 0.5$ .

How do I line up decimal numbers when subtracting?

Always line up the decimal points vertically! Write 0.9 above 0.4 with decimals aligned, then subtract normally: the answer is 0.5.

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

Remember: subtract the part from the whole! The sum (0.9) is the whole, and the known addend (0.4) is the part you already have.

Can I solve this problem a different way?

Yes! You can also count up from 0.4 to 0.9. What do you add to 0.4 to reach 0.9? The answer is still 0.5!

How do I check if my answer is correct?

Always substitute your answer back into the original equation. Does $0.4 + 0.5 = 0.9$ ? Yes! So 0.5 is correct.

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