Solve the Decimal Equation: Finding the Missing Value in 4.5 - ? = 2.1

Q: How do I subtract decimals like 4.5 - 2.1?

Line up the decimal points vertically! Write 4.5 above 2.1, making sure the decimal points are directly above each other, then subtract normally: 4.5 - 2.1 = 2.4.

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

Remember: you want what number subtracted from 4.5 gives you 2.1. So ask yourself: 4.5 minus what equals 2.1? The answer is 4.5 - 2.1 = 2.4.

Q: How can I check if 2.4 is really correct?

Substitute back into the original equation: $ 4.5 - 2.4 = 2.1 $. Since this is true, your answer of 2.4 is correct!

Q: Is there another way to think about this problem?

Yes! Think of it as: What do I need to take away from 4.5 to get 2.1? The difference between 4.5 and 2.1 is exactly what you're looking for: 2.4.

Subtraction Equations with Decimal Numbers

Fill in the missing value (?):

$4.5-?=2.1$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Choose the correct answer

00:07 Let's write down each option and check

00:11 Let's use long subtraction for calculation

00:14 Let's calculate and substitute

00:29 We see that the first option is suitable, let's move to the second

00:33 Let's use the same method again and check

00:39 Let's calculate and substitute

00:59 We see that the second option is not suitable, let's move to the third

01:03 Let's use the same method again and check

01:10 Let's calculate and substitute

01:28 We see that the third option is not suitable, let's move to the fourth

01:34 Let's use the same method again and check

01:41 Let's calculate and substitute

02:00 We see that the fourth option is not suitable

02:03 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

Fill in the missing value (?):

$4.5-?=2.1$

Step-by-step solution

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

Step 1: Identify the provided equation and rearrange it to solve for the missing number.
Step 2: Substitute the known values to isolate the missing variable.
Step 3: Perform the arithmetic operation to find the result.
Step 4: Ensure the result matches one of the given choices, confirming its correctness.

Now, let's work through each step:
Step 1: The equation given is $4.5 - ? = 2.1$ .
Step 2: Rearrange the equation to isolate the unknown:
We add '?' to both sides and subtract 2.1 from 4.5 to obtain:
$? = 4.5 - 2.1$ .
Step 3: Perform the calculation:
$4.5 - 2.1 = 2.4$ .
Step 4: Verify the answer by comparing it to the provided choices and checking the answer given:
The correct answer is indeed 2.4, which matches the given correct solution.

Therefore, the solution to the problem is $? = 2.4$ .

Final Answer

2.4

Key Points to Remember

Essential concepts to master this topic

Isolation Rule: Add unknown to both sides, subtract known value
Technique: Transform 4.5 - ? = 2.1 into ? = 4.5 - 2.1
Check: Substitute back: 4.5 - 2.4 = 2.1 ✓

Common Mistakes

Avoid these frequent errors

Subtracting in wrong order
Don't calculate 2.1 - 4.5 = -2.4! This gives a negative answer that doesn't make sense in the original equation. Always rearrange first to get ? = 4.5 - 2.1, then subtract the smaller number from the larger one.

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 can't I just subtract 2.1 from 4.5 right away?

You absolutely can! That's exactly the right approach. First rearrange to get $? = 4.5 - 2.1$ , then perform the subtraction to find 2.4.

How do I subtract decimals like 4.5 - 2.1?

Line up the decimal points vertically! Write 4.5 above 2.1, making sure the decimal points are directly above each other, then subtract normally: 4.5 - 2.1 = 2.4.

What if I get confused about which number to subtract?

Remember: you want what number subtracted from 4.5 gives you 2.1. So ask yourself: 4.5 minus what equals 2.1? The answer is 4.5 - 2.1 = 2.4.

How can I check if 2.4 is really correct?

Substitute back into the original equation: $4.5 - 2.4 = 2.1$ . Since this is true, your answer of 2.4 is correct!

Is there another way to think about this problem?

Yes! Think of it as: What do I need to take away from 4.5 to get 2.1? The difference between 4.5 and 2.1 is exactly what you're looking for: 2.4.

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