Solve the Addition Equation: Finding the Missing Value in ? + 1.2 = 2.2

Q: Why do I subtract 1.2 instead of adding it?

You need to undo what's happening to the unknown. Since 1.2 is being added to ?, you must subtract 1.2 from both sides to isolate the ?.

Q: Do I always subtract when the unknown has addition?

Yes! When you see ? + number = result, you always subtract that number from both sides. Think of it as the opposite operation cancels out what's there.

Linear Equations with Decimal Isolation

Fill in the missing value (?):

$?+1.2=2.2$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Choose the correct answer

00:03 Let's substitute each option and check

00:10 We'll use long addition for calculation

00:16 Let's calculate and substitute

00:28 We can see that the first option is not suitable, let's move to the second

00:32 Let's use the same method again and check

00:37 Let's calculate and substitute

01:00 We can see that the second option is not suitable, let's move to the third:

01:06 Let's use the same method again and check

01:14 Let's calculate and substitute

01:30 We can see that the third option is suitable, let's move to the fourth

01:35 Let's use the same method again and check

01:43 Let's calculate and substitute

02:04 We can see that the fourth option is not suitable

02:10 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 (?):

$?+1.2=2.2$

Step-by-step solution

To solve this problem, we need to find the value of the missing term in the equation $? + 1.2 = 2.2$ .

Let's proceed with the solution step by step:

Step 1: Write down the given equation: $? + 1.2 = 2.2$ .
Step 2: To isolate the unknown term (?), subtract 1.2 from both sides of the equation. This gives us:
$? = 2.2 - 1.2$
Step 3: Perform the subtraction: $2.2 - 1.2 = 1.0$ .
Step 4: Thus, the missing value is $1.0$ or simply $1$ .

Therefore, the value of the missing number is $\boxed{1}$ .

Given the multiple-choice options, the correct answer is option 3: 1.

Final Answer

Key Points to Remember

Essential concepts to master this topic

Isolation Rule: Move numbers to opposite side to find unknown value
Technique: Subtract 1.2 from both sides: $2.2 - 1.2 = 1.0$
Check: Substitute back into original equation: $1 + 1.2 = 2.2$ ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting to isolate the unknown
Don't add 1.2 to both sides when you see ? + 1.2 = 2.2! This gives you ? = 3.4, which is wrong because you're moving the wrong direction. Always subtract the number that's being added to the unknown.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I subtract 1.2 instead of adding it?

You need to undo what's happening to the unknown. Since 1.2 is being added to ?, you must subtract 1.2 from both sides to isolate the ?.

What if I get a decimal answer that's not in the choices?

Check if your decimal can be written as a whole number! For example, $1.0 = 1$ . Also, double-check your arithmetic to make sure you calculated correctly.

Do I always subtract when the unknown has addition?

Yes! When you see ? + number = result, you always subtract that number from both sides. Think of it as the opposite operation cancels out what's there.

How can I check if my answer is right?

Replace the ? with your answer in the original equation. If $1 + 1.2 = 2.2$ is true, then 1 is correct!

What if the numbers were bigger decimals?

The same method works! Just be extra careful with your decimal arithmetic. Line up the decimal points when subtracting: $2.2 - 1.2$ .

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