Solve Decimal Subtraction: Calculate 15.8 - 3.5

Decimal Subtraction with Place Value Alignment

15.83.5= 15.8-3.5=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:05 Let's solve this problem together.
00:08 We'll use long subtraction to find the answer.
00:16 Remember to place the decimal point correctly.
00:19 Start by subtracting the smallest digits first.
00:22 Keep subtracting each digit, step by step.
00:33 And that's how we solve the problem!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

15.83.5= 15.8-3.5=

2

Step-by-step solution

To solve the problem 15.83.515.8 - 3.5, we will perform decimal subtraction:

  • Step 1: Align the decimal places.
    Write the numbers so their decimal points are lined up:
    15.83.5 \quad 15.8\\ - \, 3.5\\ --------
  • Step 2: Subtract the numbers column by column.
    - Start from the rightmost digit (tenths place), 85=38 - 5 = 3. Write 33 under the line in the tenths place.
    - Move to the next left column (ones place), 53=25 - 3 = 2. Write 22 in the ones place.
    - The digit in the tens place 11 moves straight down as there is no number to subtract from.
    15.83.512.3 \quad 15.8\\ - \, 3.5\\ \underline{--------}\\ \quad 12.3
  • Step 3: Conclude with the final answer.
    The result of 15.83.515.8 - 3.5 is 12.312.3.

Therefore, the correct answer is: 12.312.3.

3

Final Answer

12.3

Key Points to Remember

Essential concepts to master this topic
  • Alignment Rule: Line up decimal points vertically before subtracting
  • Column Method: Subtract tenths first: 8 - 5 = 3, then ones: 5 - 3 = 2
  • Verification: Add your answer to subtrahend: 12.3 + 3.5 = 15.8 ✓

Common Mistakes

Avoid these frequent errors
  • Not aligning decimal points properly
    Don't line up the right edges like whole numbers = wrong place values! This makes you subtract wrong digits and get incorrect answers. Always align the decimal points vertically first, then subtract column by column.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I need to line up the decimal points?

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Lining up decimal points ensures you're subtracting like place values: tenths from tenths, ones from ones, etc. Without proper alignment, you'll subtract wrong digits and get incorrect results.

What if the numbers have different amounts of decimal places?

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Add zeros to make them the same length! For example, if subtracting 15.8 - 3.25, write it as 15.80 - 3.25. This makes alignment easier and prevents mistakes.

Do I subtract from left to right or right to left?

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Always subtract from right to left, starting with the rightmost decimal place (like hundredths, then tenths). This follows the same pattern as whole number subtraction.

How can I check if my decimal subtraction is correct?

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Use addition to check! Add your answer to the number you subtracted. If you get the original number, your subtraction is correct. For example: 12.3 + 3.5 should equal 15.8.

What if I need to borrow across the decimal point?

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Borrowing works the same way! You can borrow from the ones place to the tenths place, or from tenths to hundredths. The decimal point doesn't stop the borrowing process.

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