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Lesson 3: Subtraction within 20

# Subtracting 14 - 6

Sal subtracts 14 - 6 by first thinking about subtracting 2 and 4. Created by Sal Khan.

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• I am struggling to find a video on Subtracting within 20 with regrouping. I dont want to use blocks, I don't want to use visualizations. I want to know how to know how to write subtract 9 from 16 with regrouping.
• Try this,

We have the original number, but we can put it in expanded form*.

So, 16 = 10 + 6, and we can use this.

We know that 10 - 9 = 1, and then we can add the remaining 6 to get 7.

Expanded form is just taking the values of each number and adding them to create a number. For example, 17 = 10 + 7

You can also use this for bigger numbers
, like
1,234 = 1,000 + 200 + 30 + 4
• Hi there,

Could you please tell which video explains how to do 9-[]=5 and []-4=5.

Any help on this is much appreciated.
• Hello,
In these type of problems all you have to do is do the opposite of what it's asking. But, you would, in this case, still subtract since you are trying to find the number you subtract by and not the number you subtract from. So, 9-5=4 the missing value is 4.
For the second problem you add since you are trying to find the number you subtract from. So, 4+5=9 the missing value is 9.
Hope this helps!
• What is the commutative property? Is addition commutative?
• It is when you can change the order of an equation and get the same answer. For Ex: 4+3= 7 is the same as 3+4=7
• If your subtracting by adding a negative number does that lead to borrowing to significant to basic subtraction?
(1 vote)
• The basic concept of adding a negative number is exactly the same as subtracting that number. In higher math this may not always be the case but you will learn about those types of situations later. For now think about adding a negative number as the same process as subtraction. For example 10 + -3 = 7 and 10 - 3 = 7.
• so people can think of the four's cancelling each other out in the second problem and being left with only ten?
• Yes, but not all math problems are simple like that. But it is definitely not encouraged to think as such, as people might think that 14 - 4 = 1 if they cancel out the 4 and forget that there is a 0 behind the 1.
• Why is subtraction not commutative?