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### Course: Arithmetic (all content) > Unit 2

Lesson 4: Addition and subtraction within 20- Adding within 20 using place value blocks
- Adding within 20 using ten frames
- Adding 7 + 6
- Adding 8 + 7
- Add within 20 visually
- Add within 20
- Adding with arrays
- Adding with arrays
- Subtracting different ways
- Subtract within 20 using a number line
- Subtract within 20 using place value blocks
- Subtract within 20 using ten frames
- Subtracting 14 - 6
- Subtract within 20 visually
- Subtract within 20
- Find missing number (add and subtract within 20)
- Add & subtract within 20

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# Adding with arrays

Sal shows how to relate repeated addition to an array. Created by Sal Khan.

## Want to join the conversation?

- What is an array?(16 votes)
- Think of an array as a grid with rows and columns. For example if you look at a chessboard, you will see an 8 by 8 array of squares.

Have a wonderful day!(30 votes)

- Why can't they just do 5 times 3 instead of addition?(23 votes)
- We can use multiplication but addition is simpler form of multiplication.(27 votes)

- How would we sort 25 into an array?(11 votes)
- 5x5

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o(14 votes)

## Video transcript

- [Narrator] What we're
going to do in this video is think about how many
blocks we have here and instead of just counting them, we're gonna think about it using addition. So how do we do that? Well, we have three rows here, one, two, three rows, and each of these rows
we can see very clearly has one, two, three, four, five blocks. Same thing here in that second row, we have one, two, three,
four, five blocks. Same thing here in this third row, one, two, three, four, five. So one way to think about
the number of blocks we have, is we have
five in this first row, so that would be five, plus
five in the second row, that's another five, plus
five in the third row, plus five just like that. So if you wanna know how many blocks, it would be the same thing
as five plus five plus five. Now I know what some
of y'all are thinking, instead of just thinking
about them in terms of rows, what if we thought about
'em in terms of columns. So here we said we have five
plus five plus five blocks, but we could also think about it as, we have five columns and
each of those columns have three blocks. So that's my first column, this is my second column, this is my third column, this is my fourth column, y'all are getting the picture, this is my fifth column. And each of them have
one, two, three blocks. So this is going to be three plus three from the second column I should say, plus three from the third column, plus three from the fourth column, plus three from the fifth column. So that's interesting,
this number of blocks could also be represented
as three plus three plus three plus three plus three, which we saw is actually the same thing as five plus five plus five.