Solve the Decimal Equation: Finding the Missing Value in ? + 0.5 = 0.7

Q: Why do I subtract 0.5 instead of adding it?

Since the equation shows ? + 0.5, we need to undo that addition. The opposite of adding 0.5 is subtracting 0.5, which cancels out the +0.5 on the left side.

Q: How do I subtract decimals like 0.7 - 0.5?

Line up the decimal points vertically: 0.7-0.5____0.2Remember: 0.7 is the same as 0.70 if that helps!

Q: What does it mean to 'isolate the variable'?

Isolating the variable means getting ? by itself on one side of the equation. We want ? = some number instead of ? + something = something else.

Q: Can I check my answer a different way?

Yes! Think of it as: "What number plus 0.5 equals 0.7?" Count up from 0.5 to 0.7, and you'll see it's 0.2 more!

Decimal Equations with Basic Addition

Fill in the missing value (?):

$?+0.5=0.7$

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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 identify which of them is correct

00:08 Use vertical addition to calculate the problem

00:12 Insert one of the answers into the expression and proceed to calculate

00:25 We can see that the first option is not suitable, let's move on to the second one:

00:31 Let's apply the same method as before and proceed to check

00:37 Insert one of the answers into the expression and calculate

00:53 We can see that the second option is suitable, let's move to the third one

01:00 Once again apply the same method as before and proceed to check

01:10 Insert one of the remaining answers into the expression and calculate

01:24 We can see that the third option is not suitable, let's move to the fourth one:

01:31 Apply the same method as before and proceed to check

01:37 Insert the remaining answer into the expression and proceed to calculate

01:53 We can see that the fourth option is not suitable

02:00 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 (?):

$?+0.5=0.7$

Step-by-step solution

To solve the equation $? + 0.5 = 0.7$ , we need to isolate '?'.

Step 1: Begin with the equation $? + 0.5 = 0.7$ .
Step 2: To find '?', subtract 0.5 from both sides of the equation.
Step 3: Calculate $0.7 - 0.5$ .

Performing the subtraction:
$0.7 - 0.5 = 0.2$

Therefore, the value of '?' that makes the equation true is $0.2$ .

This corresponds to choice 2 in the options provided.

Final Answer

0.2

Key Points to Remember

Essential concepts to master this topic

Inverse Operations: Use subtraction to undo addition in equations
Technique: Subtract 0.5 from both sides: $0.7 - 0.5 = 0.2$
Check: Substitute back: $0.2 + 0.5 = 0.7$ ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting to isolate the variable
Don't add 0.5 to both sides when you see ? + 0.5 = 0.7! This gives ? = 1.2, which is wrong because you're moving in the wrong direction. Always use the opposite operation - subtract 0.5 from both sides to isolate the variable.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I subtract 0.5 instead of adding it?

Since the equation shows ? + 0.5, we need to undo that addition. The opposite of adding 0.5 is subtracting 0.5, which cancels out the +0.5 on the left side.

How do I subtract decimals like 0.7 - 0.5?

Line up the decimal points vertically:
0.7
-0.5
____
0.2
Remember: 0.7 is the same as 0.70 if that helps!

What does it mean to 'isolate the variable'?

Isolating the variable means getting ? by itself on one side of the equation. We want ? = some number instead of ? + something = something else.

Can I check my answer a different way?

Yes! Think of it as: "What number plus 0.5 equals 0.7?" Count up from 0.5 to 0.7, and you'll see it's 0.2 more!

What if I get confused about which operation to use?

Look at what's happening to the variable. If something is being added to ?, then subtract it from both sides. If something is being subtracted from ?, then add it to both sides.

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