Solve the Decimal Equation: Finding the Missing Value in 0.5 - ? = 0.2

Q: Why can't I just add 0.5 and 0.2?

Because we need to find what number was subtracted from 0.5 to get 0.2. Think of it like: 'What do I take away from 0.5 to get 0.2?' The answer is $ 0.5 - 0.2 = 0.3 $.

Q: How do I remember which number to subtract from which?

Use the pattern: if a - ? = b, then ? = a - b. So the unknown equals the first number minus the result. In our case: $ ? = 0.5 - 0.2 = 0.3 $.

Q: Can I solve this by moving numbers around?

Yes! Add the unknown to both sides: $ 0.5 - ? + ? = 0.2 + ? $, which gives $ 0.5 = 0.2 + ? $. Then subtract 0.2: $ ? = 0.5 - 0.2 = 0.3 $.

Q: How do I check if 0.3 is correct?

Substitute 0.3 back into the original equation: $ 0.5 - 0.3 = 0.2 $. Since this is true, our answer is correct!

Decimal Subtraction with Missing Numbers

Fill in the missing value (?):

$0.5-?=0.2$

❤️ Continue Your Math Journey!

We have hundreds of course questions with personalized recommendations + Account 100% premium

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

00:07 Use vertical addition to calculate the problem

00:13 Insert one of the answers into the expression and proceed to calculate

00:25 We can see that the first option doesn't fit, let's move on to the second one

00:33 Let’s apply the same method as before and proceed to check

00:40 Insert one of the answers into the expression and calculate

00:55 We can see that the second option doesn't fit, let's move on to the third one:

01:02 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

01:26 We can see that the third option fits, let's move on to the fourth one:

01:31 Insert one of the remaining answers into the expression and calculate

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

01:50 We can see that the fourth option doesn't fit

01:54 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 (?):

$0.5-?=0.2$

Step-by-step solution

To solve the problem $0.5 - ? = 0.2$ , let's proceed with the following steps:

Step 1: Begin with the equation: $0.5 - ? = 0.2$ .
Step 2: To isolate '?', add 0.2 to both sides of the equation. This gives us:

$0.5 - ? + 0.2 = 0.2 + 0.2$ .

Step 3: Simplify the equation:

$0.5 = ? + 0.2$ .

Step 4: Isolate '?' by subtracting 0.2 from 0.5:

$? = 0.5 - 0.2$ .

Step 5: Perform the subtraction:

$? = 0.3$ .

Therefore, the solution to the problem is $\boxed{0.3}$ . This matches with choice 3 of the given options.

Final Answer

0.3

Key Points to Remember

Essential concepts to master this topic

Rule: Rearrange equation to isolate the unknown value
Technique: Transform 0.5 - ? = 0.2 into ? = 0.5 - 0.2
Check: Substitute back: 0.5 - 0.3 = 0.2 ✓

Common Mistakes

Avoid these frequent errors

Adding values instead of subtracting
Don't add 0.5 + 0.2 = 0.7 to find the missing number! This gives the wrong operation entirely. Always remember: if a - ? = b, then ? = a - b, so ? = 0.5 - 0.2 = 0.3.

Practice Quiz

Test your knowledge with interactive questions

$\text{0.6+0}.5=$

FAQ

Everything you need to know about this question

Why can't I just add 0.5 and 0.2?

Because we need to find what number was subtracted from 0.5 to get 0.2. Think of it like: 'What do I take away from 0.5 to get 0.2?' The answer is $0.5 - 0.2 = 0.3$ .

How do I remember which number to subtract from which?

Use the pattern: if a - ? = b, then ? = a - b. So the unknown equals the first number minus the result. In our case: $? = 0.5 - 0.2 = 0.3$ .

Can I solve this by moving numbers around?

Yes! Add the unknown to both sides: $0.5 - ? + ? = 0.2 + ?$ , which gives $0.5 = 0.2 + ?$ . Then subtract 0.2: $? = 0.5 - 0.2 = 0.3$ .

How do I check if 0.3 is correct?

Substitute 0.3 back into the original equation: $0.5 - 0.3 = 0.2$ . Since this is true, our answer is correct!

What if I get confused about decimal subtraction?

Line up the decimal points vertically and subtract column by column. For $0.5 - 0.2$ : write 0.5 above 0.2, subtract 2 from 5 to get 3, so the answer is 0.3.

🌟 Unlock Your Math Potential

Get unlimited access to all 18 Decimal Fractions - Basic questions, detailed video solutions, and personalized progress tracking.

📹

Unlimited Video Solutions

Step-by-step explanations for every problem

📊

Progress Analytics

Track your mastery across all topics

🚫

Ad-Free Learning

Focus on math without distractions

No credit card required • Cancel anytime