Solve the Decimal Equation: Finding the Missing Value in 0.4 - ? = 0.2

Q: Why do I subtract 0.2 from 0.4 instead of the other way around?

Look at the equation structure: $ 0.4 - ? = 0.2 $. To isolate the ?, you need to move 0.2 to the other side, which gives you ? = 0.4 - 0.2.

Q: How can I remember which operation to use?

Think of it like this: "What do I subtract from 0.4 to get 0.2?" This helps you see that you need $ 0.4 - 0.2 = 0.2 $.

Q: What if I got 0.6 as my answer?

If you got 0.6, you probably added instead of subtracted. Check: $ 0.4 - 0.6 = -0.2 $, not 0.2! Always verify your answer.

Q: Why does the missing value equal one of the given numbers?

This is just a coincidence in this problem! The missing value could be any decimal. What matters is following the correct steps to solve the equation.

Decimal Subtraction with Missing Minuend

Fill in the missing value (?):

$0.4-?=0.2$

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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

00:09 Use vertical addition to calculate the problem

00:17 Insert one of the answers into the expression and proceed to calculate

00:31 We can see that the first option doesn't fit, let's move on to the second one

00:34 Let’s apply the same method as before and proceed to check

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

01:02 The second option fits, let's move on to the third one

01:09 Once again apply the same method as before and proceed to check

01:16 Insert one of the remaining answers into the expression and calculate

01:31 We can see that the third option doesn't fit, let's move on to the fourth one:

01:39 Apply the same method as before and proceed to check

01:44 Insert the remaining answer into the expression and proceed to calculate

02:04 We can see that the fourth option doesn't fit

02:09 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 (?):

$0.4-?=0.2$

Step-by-step solution

To solve this problem, we'll find the missing value using simple subtraction as follows:

Step 1: Identify the equation given: $0.4 - ? = 0.2$ .
Step 2: Rearrange the equation to solve for ?:
$? = 0.4 - 0.2$
Step 3: Perform the subtraction:
$0.4 - 0.2 = 0.2$
The missing value that satisfies the equation is $0.2$ .

From the choices provided, the correct answer is choice 2: 0.2.

Final Answer

0.2

Key Points to Remember

Essential concepts to master this topic

Rule: Rearrange equation to isolate the missing value
Technique: Convert 0.4 - ? = 0.2 to ? = 0.4 - 0.2
Check: Substitute back: 0.4 - 0.2 = 0.2 ✓

Common Mistakes

Avoid these frequent errors

Adding instead of subtracting to find the missing value
Don't add 0.4 + 0.2 = 0.6 thinking you need to combine the given numbers! This gives a wrong answer because you're not solving the original equation. Always rearrange the equation properly: ? = 0.4 - 0.2.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I subtract 0.2 from 0.4 instead of the other way around?

Look at the equation structure: $0.4 - ? = 0.2$ . To isolate the ?, you need to move 0.2 to the other side, which gives you ? = 0.4 - 0.2.

How can I remember which operation to use?

Think of it like this: "What do I subtract from 0.4 to get 0.2?" This helps you see that you need $0.4 - 0.2 = 0.2$ .

What if I got 0.6 as my answer?

If you got 0.6, you probably added instead of subtracted. Check: $0.4 - 0.6 = -0.2$ , not 0.2! Always verify your answer.

Is there a visual way to understand this?

Yes! Think of it on a number line: start at 0.4, move backward to land on 0.2. The distance you moved is your missing value (0.2).

Why does the missing value equal one of the given numbers?

This is just a coincidence in this problem! The missing value could be any decimal. What matters is following the correct steps to solve the equation.

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