Solve the Decimal Equation: Finding the Missing Addend in 0.4 + __ = 0.51

Q: Why do I subtract 0.4 from 0.51 instead of adding them?

Think of it like this: if you have part + missing part = whole, then missing part = whole - part. Since $ 0.4 + \text{missing} = 0.51 $, the missing number equals $ 0.51 - 0.4 $.

Q: How do I subtract 0.4 from 0.51 when they have different decimal places?

Line up the decimal points! Write it as $ 0.51 - 0.40 $ by adding a zero. Now subtract: 1 - 0 = 1 in hundredths place, 5 - 4 = 1 in tenths place.

Q: How can I check if 0.11 is really correct?

Substitute back into the original equation: $ 0.4 + 0.11 = 0.51 $. Since both sides are equal, 0.11 is correct!

Decimal Addition with Missing Addends

$0.4+_{——}=0.51$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Find the unknown

00:04 Isolate the unknown

00:09 Use long subtraction for calculation

00:12 Subtract and substitute accordingly

00:19 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

$0.4+_{——}=0.51$

Step-by-step solution

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

Step 1: Identify the given information
Step 2: Use subtraction to find the missing value
Step 3: Verify the correct answer among the choice options

Now, let's work through each step:
Step 1: The problem gives us $0.4 + \_\_\_ = 0.51$ . We need to find the missing number.
Step 2: To find the missing number, subtract $0.4$ from $0.51$ :
$0.51 - 0.4 = 0.11$

Step 3: Verify this result matches one of the provided answer choices.
The missing number is $0.11$ , which corresponds to choice $0.11$ .

Therefore, the solution to the problem is $0.11$ .

Final Answer

$0.11$

Key Points to Remember

Essential concepts to master this topic

Rule: To find missing addend, subtract known addend from sum
Technique: Calculate $0.51 - 0.4 = 0.11$ to find missing value
Check: Verify by adding: $0.4 + 0.11 = 0.51$ ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting to find the missing addend
Don't add 0.4 + 0.51 = 0.91 to find the missing number! This gives you the wrong operation and a completely incorrect answer. Always subtract the known addend from the sum to find the missing addend.

Practice Quiz

Test your knowledge with interactive questions

Determine whether the exercise is written correctly in relation to the position of the decimal point:

FAQ

Everything you need to know about this question

Why do I subtract 0.4 from 0.51 instead of adding them?

Think of it like this: if you have part + missing part = whole, then missing part = whole - part. Since $0.4 + \text{missing} = 0.51$ , the missing number equals $0.51 - 0.4$ .

How do I subtract 0.4 from 0.51 when they have different decimal places?

Line up the decimal points! Write it as $0.51 - 0.40$ by adding a zero. Now subtract: 1 - 0 = 1 in hundredths place, 5 - 4 = 1 in tenths place.

What if I get a different answer like 0.10 or 0.12?

Double-check your subtraction! Common errors include forgetting to align decimal points or making arithmetic mistakes. Always verify by adding your answer to 0.4 to see if you get 0.51.

How can I check if 0.11 is really correct?

Substitute back into the original equation: $0.4 + 0.11 = 0.51$ . Since both sides are equal, 0.11 is correct!

Is there a faster way to solve this type of problem?

Once you understand the pattern, missing addend problems become quick! Just remember: missing addend = sum - known addend. With practice, you can solve these mentally.

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