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## 7th grade foundations (Eureka Math/EngageNY)

### Course: 7th grade foundations (Eureka Math/EngageNY)>Unit 2

Lesson 3: Topic C: Foundations

# Subtracting decimals: 39.1 - 0.794

Learn to subtract decimals by aligning the decimal points and place values. Regroup numbers for easier subtraction, and then perform the subtraction for each place value. Mastering decimal subtraction helps build strong math skills and real-world problem-solving abilities. Created by Sal Khan.

## Want to join the conversation?

• 0 is one of the most important numbers but we don't realize it.
• The number 0 has special properties. Any number plus 0 is itself, any number minus 0 is itself, 0 minus any number is the number’s opposite, any number times 0 is 0, 0 divided by any nonzero number is 0, any nonzero number divided by 0 is undefined (positively or negatively infinite), and 0 divided by 0 is indeterminate.

In algebra, getting 0 on one side of a quadratic equation (that is, an equation with 2 as the highest exponent on the variable) is necessary in order to solve the quadratic by factoring or using the quadratic formula.

If you decide to study calculus later on, you will see that derivatives (slopes) of functions are set equal to 0 in order maximize or minimize functions. You will also frequently encounter the indeterminate expression 0/0 in limit problems.

If you decide to take linear algebra or analysis later on, you will see that 0 comes up amazingly often!
• when we add subtract multiply do we line up the deciml points
• Subtracting decimals uses the same setup as adding decimals: line up the decimal points, and then subtract. In cases where you are subtracting two decimals that extend to different place values, it often makes sense to add extra zeros to make the two numbers line up—this makes the subtraction a bit easier to follow.
• In the video Sal shows the hundredths place borrows 1 tenth from 11 tenths in the tenths place, then the hundredths place turns out 10 tenths, shouldn't it be 1 tenth? Because we are taken just 1 tenth, the tenths place got 10 tenths after that, because of the hundredths place took just 1 tenth. What is the explanation?
• Basically you know the tenths place and hundredths place on a decimal? 0.12, 1 is the tenth place and two is the hundredth. This goes the same for fractions. 1/100 you say it as one hundredth same goes for the hundredth in the example decimal (0.12) except the hundredth is 2 so it'd be equivalent to 2/100. Does that help?
• Is there a good video to watch explaining how to borrow from 0s, Sal seemed to do it from the left to the right and I've always learned to do it opposite, but I get these problems wrong because of one or two letters. Thanks!
• I'm not entirely sure if there's a separate video just for borrowing from zeros but I wouldn't be surprised if there was! I can give you the basic rundown.

When you borrow from a zero, you aren't actually borrowing from that zero. In fact, that zero borrows from the number next to it. Here's an example:

5.09 - 2.29 = ?

Here, you can see that 0 is needed to 'borrow' from 5 so that 2 can be subtracted from 0. Since 0 borrowed from a number that you need to multiply the place to the left (from the 5's 'point of view') 10 times to get the place you're in. So, now you have

4. {10}9
3. 29 -
-----------
1.80

And you have your answer! Sorry if it was a bit confusing. Hope it helped though!

Keep learning,
Chocomuff
• when were numbers first used in history?
• see www.vedicsciences.net/articles/history-of-numbers.html
• Will you ever have 2 numbers that will have 2 decimals. For example: 123.456.778
• No, but in foreign countries, instead of commas to separate thousands, they use decimals.
(1 vote)
• At what is it talking about he said " If we make this " make what sal?
• Lmao!
(1 vote)
• I turned my dog to a microwave