Solve: Finding the Missing Number in 0.31 - _ = 0.2

Q: Why do we rearrange the equation instead of just guessing?

Rearranging gives you the exact mathematical method to find the answer! Guessing might work sometimes, but algebra ensures you get the right answer every time.

Q: How do I line up the decimals when subtracting?

Always line up the decimal points vertically! For 0.31 - 0.2, write it as 0.31 - 0.20 so both numbers have the same decimal places.

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

Remember the pattern: Start - Missing = Result becomes Missing = Start - Result. So from $ 0.31 - x = 0.2 $, you get $ x = 0.31 - 0.2 $.

Q: Can I check my answer a different way?

Yes! You can also think: "What plus 0.2 equals 0.31?" Since 0.11 + 0.2 = 0.31, you know 0.11 is correct!

Q: Why is 0.31 - 0.2 equal to 0.11 and not 0.29?

Be careful with decimal place values! $ 0.31 $ has 31 hundredths, and $ 0.2 $ has 20 hundredths. So 31 - 20 = 11 hundredths = $ 0.11 $.

Decimal Subtraction with Missing Minuend

$0.31-_{——}=0.2$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Find the unknown

00:05 Isolate the unknown

00:09 Use long subtraction for calculation

00:13 Subtract and substitute accordingly

00:23 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

$0.31-_{——}=0.2$

Step-by-step solution

To solve this problem, we'll follow these steps:

Subtract the given number from 0.31 to find the missing portion.
Ensure accurate decimal subtraction.

Let's perform the calculation:
The given equation is $0.31 - x = 0.2$ .
We want to find $x$ . Rearranging gives us $x = 0.31 - 0.2$ .
Perform the subtraction:

$0.31 - 0.2 = 0.11$

The correct answer is $x = 0.11$ .

Therefore, the solution to the problem is $0.11$ .

Final Answer

0.11

Key Points to Remember

Essential concepts to master this topic

Rearrangement Rule: To find missing subtrahend, subtract result from minuend
Technique: From $0.31 - x = 0.2$ , get $x = 0.31 - 0.2 = 0.11$
Check: Substitute back: $0.31 - 0.11 = 0.2$ matches the original equation ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting to find the missing number
Don't add 0.31 + 0.2 = 0.51! This gives a completely wrong answer because you're going in the opposite direction. Always remember: if the equation shows subtraction, you find the missing part by subtracting the result from the starting number.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do we rearrange the equation instead of just guessing?

Rearranging gives you the exact mathematical method to find the answer! Guessing might work sometimes, but algebra ensures you get the right answer every time.

How do I line up the decimals when subtracting?

Always line up the decimal points vertically! For 0.31 - 0.2, write it as 0.31 - 0.20 so both numbers have the same decimal places.

What if I get confused about which number to subtract from which?

Remember the pattern: Start - Missing = Result becomes Missing = Start - Result. So from $0.31 - x = 0.2$ , you get $x = 0.31 - 0.2$ .

Can I check my answer a different way?

Yes! You can also think: "What plus 0.2 equals 0.31?" Since 0.11 + 0.2 = 0.31, you know 0.11 is correct!

Why is 0.31 - 0.2 equal to 0.11 and not 0.29?

Be careful with decimal place values! $0.31$ has 31 hundredths, and $0.2$ has 20 hundredths. So 31 - 20 = 11 hundredths = $0.11$ .

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