Solve the Decimal Equation: Finding the Missing Value in ? + 2.4 = 4.5

Q: Why do I subtract 2.4 from 4.5 instead of the other way around?

In the equation $ ? + 2.4 = 4.5 $, we want to isolate the missing number. Since 2.4 is being added, we do the opposite operation (subtract) to both sides.

Q: How do I line up the decimal points correctly?

Write the numbers vertically with decimal points directly under each other:4.5-2.4____This ensures you subtract tenths from tenths and ones from ones.

Q: How can I check if my answer is right?

Substitute your answer back into the original equation. If $ 2.1 + 2.4 = 4.5 $, then you're correct! Addition and subtraction are inverse operations.

Q: Do I always subtract the smaller number from the larger one?

No! In equations, subtract based on what you need to isolate the variable. Here we subtract 2.4 from 4.5 because we're solving for the missing addend.

Decimal Subtraction with Missing Addends

Fill in the missing value (?):

$?+2.4=4.5$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Identify which of the following answers is correct

00:03 Insert each of the potential answers into the expression in order to identify which of them is correct

00:10 Use vertical addition to calculate the problem

00:17 Insert one of the answers into the expression and proceed to calculate

00:31 We can see that the first option is not suitable, let's move on to the second one

00:36 Let's apply the same method as before and proceed to check

00:45 Insert one of the answers into the expression and calculate

01:00 We can see that the second option is suitable, let's move on to the third one

01:06 Once again apply the same method as before and proceed to check

01:15 Insert one of the remaining answers into the expression and calculate

01:29 We can see that the third option is not suitable, let's move to the fourth one:

01:36 Apply the same method as before and proceed to check

01:43 Insert the remaining answer into the expression and proceed to calculate

01:58 We can see that the fourth option is not suitable

02:04 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Fill in the missing value (?):

$?+2.4=4.5$

Step-by-step solution

Let's solve the problem step by step:

Step 1: Identify the equation.
The equation is $? + 2.4 = 4.5$ .
Step 2: Isolate the missing value.
To find the missing number, subtract 2.4 from both sides.
Step 3: Perform the subtraction.
The calculation is $4.5 - 2.4$ .
Step 4: Calculate the difference.
Start with the tenths place: $5 - 4 = 1$ in the tenths place.
Subtract the whole numbers: $4 - 2 = 2$ . Thus, the complete subtraction is $2.1$ .

Therefore, the missing value that satisfies the equation $? + 2.4 = 4.5$ is $2.1$ .

Final Answer

2.1

Key Points to Remember

Essential concepts to master this topic

Inverse Operations: Use subtraction to undo addition in equations
Technique: Subtract 2.4 from 4.5: align decimals and calculate
Check: Verify 2.1 + 2.4 = 4.5 by adding back ✓

Common Mistakes

Avoid these frequent errors

Not aligning decimal points during subtraction
Don't subtract 4.5 - 2.4 without aligning decimals = wrong answer like 2.9! When decimal points aren't lined up, you subtract wrong place values. Always align decimal points vertically before subtracting.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I subtract 2.4 from 4.5 instead of the other way around?

In the equation $? + 2.4 = 4.5$ , we want to isolate the missing number. Since 2.4 is being added, we do the opposite operation (subtract) to both sides.

How do I line up the decimal points correctly?

Write the numbers vertically with decimal points directly under each other:

4.5
-2.4
____

This ensures you subtract tenths from tenths and ones from ones.

What if I need to borrow when subtracting decimals?

Just like with whole numbers! If you need to subtract a larger digit, borrow from the next place value. Remember: borrowing 1 from the ones place gives you 10 tenths.

How can I check if my answer is right?

Substitute your answer back into the original equation. If $2.1 + 2.4 = 4.5$ , then you're correct! Addition and subtraction are inverse operations.

Do I always subtract the smaller number from the larger one?

No! In equations, subtract based on what you need to isolate the variable. Here we subtract 2.4 from 4.5 because we're solving for the missing addend.

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