Solve (-0.43)-(-0.87): Subtracting Negative Decimals

Q: Why does subtracting a negative become addition?

Think of it as removing a debt! If you owe $0.87 and that debt is taken away, you actually gain $0.87. So $ -(-0.87) = +0.87 $.

Q: How do I remember the double negative rule?

Use the phrase: "Two negatives make a positive". When you see two negative signs together, they always become a plus sign.

Q: Should I line up the decimals when adding?

Yes! Write it as:$ \begin{align} 0.87 \\ - 0.43 \\ \hline 0.44 \end{align} $This prevents decimal place errors.

Q: How can I check my work?

Substitute back: If your answer is 0.44, then $ (-0.43) - (-0.87) $ should equal $ -0.43 + 0.87 = 0.44 $ ✓

Decimal Subtraction with Double Negatives

$(-0.43)-(-0.87)=$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Solve

00:03 Negative times negative is always positive

00:08 We will use long subtraction for calculation

00:16 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

$(-0.43)-(-0.87)=$

Step-by-step solution

Let's first consider the rule:

$-(-x)=+x$

Now let's write the exercise in the appropriate form:

$-0.43+0.87=$

We'll use the distributive property and solve the exercise step by step:

$0.87\\-0.43\\0.44$

Final Answer

$0.44$

Key Points to Remember

Essential concepts to master this topic

Rule: Subtracting a negative equals adding the positive value
Technique: Convert (-0.43)-(-0.87) to -0.43+0.87, then compute 0.87-0.43
Check: Verify 0.44: (-0.43)+0.44 = 0.01, not equal to 0.87 ✓

Common Mistakes

Avoid these frequent errors

Treating both negatives as subtraction
Don't compute (-0.43)-(-0.87) as 0.43-0.87 = -0.44! This ignores the double negative rule completely. Always remember that subtracting a negative means adding the positive: -(-0.87) becomes +0.87.

Practice Quiz

Test your knowledge with interactive questions

$$ -5-(-2)= $$

FAQ

Everything you need to know about this question

Why does subtracting a negative become addition?

Think of it as removing a debt! If you owe $0.87 and that debt is taken away, you actually gain $0.87. So $-(-0.87) = +0.87$ .

How do I remember the double negative rule?

Use the phrase: "Two negatives make a positive". When you see two negative signs together, they always become a plus sign.

Should I line up the decimals when adding?

Yes! Write it as:
$\begin{align} 0.87 \\ - 0.43 \\ \hline 0.44 \end{align}$
This prevents decimal place errors.

What if I got -1.3 as my answer?

You probably added the numbers instead of applying the double negative rule first. Remember: $(-0.43) - (-0.87) \neq (-0.43) + (-0.87)$ .

How can I check my work?

Substitute back: If your answer is 0.44, then $(-0.43) - (-0.87)$ should equal $-0.43 + 0.87 = 0.44$ ✓

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