Solve the Decimal Equation: Finding the Missing Value in 1.2 - ? = 1.1

Q: Why do I move 1.1 to the other side?

When you have $ 1.2 - ? = 1.1 $, you need to isolate the unknown. Moving 1.1 to the right side by adding it to both sides gives you $ ? = 1.2 - 1.1 $.

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

Remember the pattern: If $ A - ? = B $, then $ ? = A - B $. So from $ 1.2 - ? = 1.1 $, you always subtract the result (1.1) from the starting number (1.2).

Q: How do I line up decimals when subtracting?

Align the decimal points vertically! Write 1.2 above 1.1 with decimal points in the same column, then subtract normally: 1.2 - 1.1 = 0.1.

Q: Can I check my answer a different way?

Yes! You can also think: "What do I add to 1.1 to get 1.2?" Since 1.1 + 0.1 = 1.2, the missing value must be 0.1.

Q: What if the missing value was in a different position?

The method changes! If you had $ ? - 0.1 = 1.1 $, then $ ? = 1.1 + 0.1 = 1.2 $. Always identify which number is missing first.

Decimal Subtraction with Missing Subtrahends

Fill in the missing value (?):

$1.2-?=1.1$

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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 verify which of them is correct

00:08 Use vertical addition to calculate the problem

00:14 Insert one of the answers into the expression and proceed to calculate

00:38 We can see that the first option doesn't fit, let's move on to the second one:

00:43 Let’s apply the same method as before and proceed to check

00:49 Insert one of the answers into the expression and calculate

01:01 We can see that the second option doesn't fit, let's move on to the third one:

01:07 Once again apply the same method as before and proceed to check

01:14 Insert one of the remaining answers into the expression and calculate

01:29 We can see that the third option fits, let's move on to the fourth one:

01:33 Apply the same method as before and proceed to check

01:41 Insert the remaining answer into the expression and proceed to calculate

01:58 We can see that the fourth option doesn't fit

02:01 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 (?):

$1.2-?=1.1$

Step-by-step solution

To solve the problem $1.2 - ? = 1.1$ , we need to identify the unknown value represented by the question mark.

Let's go through the solution step-by-step:

Step 1: Rewrite the equation in terms of subtraction: $1.2 - x = 1.1$ , where $x$ is the missing value.
Step 2: Rearrange the equation to solve for $x$ : $x = 1.2 - 1.1$ .
Step 3: Perform the subtraction: $x = 0.1$ .
Step 4: Check the solution by substituting back into the original equation: $1.2 - 0.1 = 1.1$ , which is correct.

Therefore, the solution to the problem is that the missing value is $0.1$ .

Given the choices, the correct option is: $0.1$

Final Answer

0.1

Key Points to Remember

Essential concepts to master this topic

Rearrangement Rule: Transform subtraction into addition by moving terms across equals
Technique: Calculate $x = 1.2 - 1.1 = 0.1$ to find missing value
Check: Verify by substituting back: $1.2 - 0.1 = 1.1$ ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting when rearranging
Don't calculate 1.2 + 1.1 = 2.3 as the missing value! This happens when you forget the subtraction becomes addition during rearrangement. Always remember: from 1.2 - ? = 1.1, you get ? = 1.2 - 1.1, not 1.2 + 1.1.

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 move 1.1 to the other side?

When you have $1.2 - ? = 1.1$ , you need to isolate the unknown. Moving 1.1 to the right side by adding it to both sides gives you $? = 1.2 - 1.1$ .

What if I get confused about which number to subtract?

Remember the pattern: If $A - ? = B$ , then $? = A - B$ . So from $1.2 - ? = 1.1$ , you always subtract the result (1.1) from the starting number (1.2).

How do I line up decimals when subtracting?

Align the decimal points vertically! Write 1.2 above 1.1 with decimal points in the same column, then subtract normally: 1.2 - 1.1 = 0.1.

Can I check my answer a different way?

Yes! You can also think: "What do I add to 1.1 to get 1.2?" Since 1.1 + 0.1 = 1.2, the missing value must be 0.1.

What if the missing value was in a different position?

The method changes! If you had $? - 0.1 = 1.1$ , then $? = 1.1 + 0.1 = 1.2$ . Always identify which number is missing first.

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