Subtracting decimals (old) | Decimals | Pre-Algebra | Khan Academy | Summary and Q&A

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January 23, 2007
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Khan Academy
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Subtracting decimals (old) | Decimals | Pre-Algebra | Khan Academy

TL;DR

Learn how to subtract decimal numbers by lining up the decimals, borrowing when necessary, and performing normal subtraction.

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Questions & Answers

Q: How do you line up decimals when subtracting decimal numbers?

To line up decimals, place the decimal point of the numbers directly under each other. This ensures that the place values are aligned correctly for subtraction.

Q: Why do we add zeros when subtracting decimal numbers?

We add zeros so that we have digits to subtract from in every place value. This ensures that each digit on the top can be subtracted from a corresponding digit on the bottom.

Q: Can you explain the borrowing process when subtracting decimals?

When borrowing, start from the rightmost digit and check if the top digit is smaller than the bottom digit. If it is, borrow from the digit to the left. Continue this process until all the digits can be subtracted properly.

Q: What is the purpose of borrowing from the digit to the left instead of borrowing from a zero?

Borrowing from the digit to the left instead of a zero makes the process more intuitive and helps avoid confusion. It ensures that each digit is borrowed from a specific number and maintains the correct place value.

Summary & Key Takeaways

  • The video explains how to subtract decimal numbers by aligning the decimals, adding zeros, and borrowing when necessary.

  • Borrowing is done by borrowing from the digit to the left instead of borrowing from a zero.

  • The key to mastering subtraction of decimals is to understand and practice borrowing correctly.

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