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## Early math review

# Number grid

Sal goes through all the numbers from 0 to 100 and shows some interesting patterns. Created by Sal Khan and Arshya Vahabzadeh.

## Video transcript

Voiceover: The goal of this video
is to essentially write down all the numbers in order
from zero to a 100. But I’m going to do it in
an interesting way, a way that maybe will allow
us to see some patterns in the numbers themselves. So let me just start, so I’m
gonna start at zero, one, two, three, four, five, six,
seven. eight, and nine, and instead of, of course we
know the next number is 10, which I could write down
but instead of doing that I’m just going to copy
and paste all of this. So copy and paste all of that
and see what this does for us. So if I do that, how does that help us? Well we know the next number is 10, which one way to think about it is, it’s a one followed by a zero. What’s the number after that? Well it’s 11, which is
a one followed by a one. What’s the number after that? Well it’s a 12, which is
a one followed by a two, and then 13, 14, 15, 16, 17, 18, and 19. Well that was pretty neat. This next row of numbers
as I went from 10 to 19 looked just like the first ones, so the 2nd number is the same in yellow, but then I added a purple
one to the front of it. And one way to think about
it is, each of these numbers, the purple one that I
added, that represents 10. So 11 could be viewed as 10 plus one, 12 could be viewed as 10 plus two. Let’s see if this keeps working. So let’s take another row of numbers. So let’s take another
row , my original row, and what do I get to after 19? Well of course after 19 we get to 20. So 20, two zero and then 21,
22, 23, 24, 25, 26, 27, 28, 29. I think you might start
to see the pattern here. What are we gonna do for the next row? Well now we’re in the 30s. So the first number 30 is 30 plus zero, 30 plus one, 30 plus two,
30 plus three which is 33, 34, 35, 36, 37, 38, 39. So just doing that I think
you already see the pattern. The number on the right we
keep going from zero, one, two, three, four, five, six, seven, eight, nine, and then
the number on the left, if we’re between 10 and 19,
you’ll always have a one. If you’re between 20 and 29,
you’ll always have a two. If you’re between 30 and 39,
you’ll always have a three. Now how can I complete this going all the way to 99 pretty fast? Well let’s do that, so
that’s going to be my 40s, I haven’t written it out yet. That’s going to be my 50s,
this is going to be my 60s, 70s, 80s, and then I have
my 90s right over here. And so this one we already said
this is going to be my 40s, this is going to be my
50s, this is going to be, I’m trying to make sure I
use all my colors, my 60s, this is going to be my 70s,
and then I have my 80s, and then of course I have
my, let me do a color that, I’ll re-use magenta, I’ll have my 90s. So what if I woulda just take this, so let me just take this right over here, and copy and paste that. So copy, and then let me paste it. So now I have 41, 51, 61, 71, 81, and 91. Now I can do it over here,
42, 52, 62, 72, 82, and 92. And I can do it for each of
these, for each of these now. So that’s, now, 44,
54, 64, 74, 84, and 94. And so when I do that
we see the full pattern. We see the full pattern
and I’m almost done. I’m almost done filling in
my numbers from zero to 99. 49, 59,69,79,89,99 and if
we just wanna feel good, we could throw in, we
could throw in a 100, a 100 right over there. And you’ll see the pattern
still holds, we went from one, two, three, four, five,
six, seven, eight, nine, and now we got to 10 followed by a zero. That was pretty neat.