Solve the Decimal Equation: Finding the Number in x - 0.8 = 0.1

Q: Why do I add 0.8 to both sides instead of subtracting it?

You need to undo the subtraction in the equation. Since we have minus 0.8, we add 0.8 to both sides to cancel it out and isolate the unknown variable.

Q: How do I add decimals like 0.1 + 0.8?

Line up the decimal points vertically:0.1+ 0.8= 0.9Just add normally and keep the decimal point in the same position!

Q: Can I check my answer a different way?

Yes! You can also think: "What number minus 0.8 equals 0.1?" Since $ 0.9 - 0.8 = 0.1 $, the answer is 0.9.

Q: What if my answer doesn't look right?

Always substitute back into the original equation! Replace the ? with your answer and see if both sides are equal. If not, double-check your decimal addition.

Linear Equations with Decimal Addition

Fill in the missing value (?):

$?-0.8=0.1$

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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

00:11 Use vertical addition to calculate the problem

00:18 Insert one of the answers into the expression and proceed to calculate

00:32 We can see that the first option doesn't fit, let's move on to the second one:

00:40 Let’s apply the same method as before and proceed to check

00:44 Insert one of the answers into the expression and calculate

00:54 We can see that the second option fits, let's move on to the third one

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

01:06 Insert one of the remaining answers into the expression and calculate

01:19 We can see that the third option doesn't fit, let's move on to the fourth one

01:26 Apply the same method as before and proceed to check

01:31 Insert the remaining answer into the expression and proceed to calculate

01:56 We can see that the fourth option doesn't fit

02:02 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 (?):

$?-0.8=0.1$

Step-by-step solution

Let's solve the equation $? - 0.8 = 0.1$ by isolating the unknown variable:

Step 1: Write the equation:

$? - 0.8 = 0.1$

Step 2: To find the value of '?', add $0.8$ to both sides of the equation as follows:

$? - 0.8 + 0.8 = 0.1 + 0.8$

Step 3: Simplify both sides:

The left side simplifies to $?$ because $-0.8 + 0.8 = 0$ .

The right side becomes $0.1 + 0.8 = 0.9$ .

So, $? = 0.9$ .

Therefore, the missing value is $0.9$ .

Final Answer

0.9

Key Points to Remember

Essential concepts to master this topic

Isolation Rule: Add the same value to both sides to isolate the variable
Technique: Add 0.8 to both sides: 0.1 + 0.8 = 0.9
Check: Substitute back: 0.9 - 0.8 = 0.1 ✓

Common Mistakes

Avoid these frequent errors

Subtracting instead of adding the constant term
Don't subtract 0.8 from 0.1 to get -0.7! This gives the wrong operation and negative result. Always perform the opposite operation: if the equation has subtraction, add to both sides.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I add 0.8 to both sides instead of subtracting it?

You need to undo the subtraction in the equation. Since we have minus 0.8, we add 0.8 to both sides to cancel it out and isolate the unknown variable.

What if I forgot which operation to use?

Look at what's happening to your variable! If something is being subtracted from it, you add to undo it. If something is being added to it, you subtract to undo it.

How do I add decimals like 0.1 + 0.8?

Line up the decimal points vertically:

0.1
+ 0.8
= 0.9

Just add normally and keep the decimal point in the same position!

Can I check my answer a different way?

Yes! You can also think: "What number minus 0.8 equals 0.1?" Since $0.9 - 0.8 = 0.1$ , the answer is 0.9.

What if my answer doesn't look right?

Always substitute back into the original equation! Replace the ? with your answer and see if both sides are equal. If not, double-check your decimal addition.

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