Solve Decimal Addition: Finding Missing Number in 0.31 + _ = 0.45

Q: Why do I subtract 0.31 from 0.45 instead of the other way around?

Think of it like this: Sum - Known Part = Missing Part. Since 0.45 is the total and 0.31 is what we already have, we subtract to find what's missing!

Q: How do I line up decimals when subtracting?

Always line up the decimal points vertically! Write 0.45 above 0.31 with decimal points aligned, then subtract normally from right to left.

Q: Can I use mental math for this?

Absolutely! Think: 31 + what = 45? Count up from 31 to 45, or recognize that 45 - 31 = 14, so 0.45 - 0.31 = 0.14.

Q: How do I check if 0.14 is really correct?

Substitute back into the original: $ 0.31 + 0.14 $. Add them up: 0.45. Since this matches the right side of the equation, 0.14 is correct!

Inverse Operations with Decimal Subtraction

$0.31+_{——}=0.45$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:05 Let's start by finding the unknown value.

00:09 Now, we want to isolate the unknown variable.

00:15 We'll use long subtraction here to help us calculate.

00:19 Subtract the numbers, then substitute the result.

00:26 And that's how we find the solution to our question!

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

$0.31+_{——}=0.45$

Step-by-step solution

To solve the problem, we need to determine the value of the missing number that completes the equation $0.31 + \_ = 0.45$ .

We'll follow these steps:

Subtract $0.31$ from $0.45$ to find the missing number.

Now, let's work through the solution:

Step 1: Perform the subtraction:

$0.45 - 0.31 = 0.14$

Therefore, the missing number is $0.14$ . This is the value that, when added to $0.31$ , results in $0.45$ .

The correct choice from the given options is $0.14$ .

Final Answer

$0.14$

Key Points to Remember

Essential concepts to master this topic

Rule: Missing addend equals sum minus known addend
Technique: Subtract $0.31$ from $0.45$ to get $0.14$
Check: Add your answer back: $0.31 + 0.14 = 0.45$ ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting to find missing number
Don't add 0.31 + 0.45 = 0.76! This gives you the wrong operation and creates a number too large to fit the equation. Always subtract the known addend from the sum to find the missing addend.

Practice Quiz

Test your knowledge with interactive questions

$\text{0.6+0}.5=$

FAQ

Everything you need to know about this question

Why do I subtract 0.31 from 0.45 instead of the other way around?

Think of it like this: Sum - Known Part = Missing Part. Since 0.45 is the total and 0.31 is what we already have, we subtract to find what's missing!

How do I line up decimals when subtracting?

Always line up the decimal points vertically! Write 0.45 above 0.31 with decimal points aligned, then subtract normally from right to left.

What if I get a negative answer?

If your answer is negative, you probably subtracted in the wrong direction. Remember: larger number minus smaller number gives the missing addend.

Can I use mental math for this?

Absolutely! Think: 31 + what = 45? Count up from 31 to 45, or recognize that 45 - 31 = 14, so 0.45 - 0.31 = 0.14.

How do I check if 0.14 is really correct?

Substitute back into the original: $0.31 + 0.14$ . Add them up: 0.45. Since this matches the right side of the equation, 0.14 is correct!

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