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

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Determine whether the exercise is correctly written or not.

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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