Intro to Roman numerals | Class 6 (India) | Math | Khan Academy

- [Instructor] I remember
when I was in school,

I learnt numbers as one,
two, three, and so on,

but then when I saw my class board

it has class one written on it.

You know, first standard,

and sometimes we call it
STD, so first standard.

And then second standard was
not written as two, but two I's

and, you know, second standard.

Third standard was written like this,

fourth was written like
this, an I and a V,

and I did not understand
what was going on.

So I asked my teacher, "What are these?

"Why are we writing,

"why aren't we writing just
second standard like this?"

And she said, "Oh, these
that you're used to

"they are Hindu Arabic numerals,

"the ones that we usually use,

"but there are other kinds of numerals

"called Roman numerals."

And that got me really curious

and also a little bit confused.

I was asking why are there more than

one ways to write numbers

and if these are Roman numerals,

why don't we use them anymore?

And of course what are
they in the first place?

And why should I even learn them?

That was main question,

so why should I know one
more way of writing numbers

when I just have one already?

And the more I learned about
it I realized that it was

learning about Roman
numerals is sort of like

visiting a math museum.

If you have gone to a
normal or a usual museum

you might be used to seeing
dinosaurs or their skeletons.

I've seen some fossils as well.

And this shows that the
way the world is today

is not the way it always was.

We had other ways of doing things

which we don't do anymore.

And I realized that Roman numerals,

or learning Roman numerals,
is similar to that.

We can go back in time and
see how we used to count

and even think about questions like

why we don't count like that anymore

and is what we're doing
today better and if so, how?

So I learnt more about Roman numeral.

I had these alphabets
denoting some numbers.

Just like in my usual numbers

I have one, two, three,
four, or what I call,

when I say usual I mean
the Hindu Arabic numerals.

I have one, two, three, four, five,

six, seven, eight, nine.

These are my digits and
using these I can make

every other number possible,

so these are the digits of
the Hindu Arabic system.

Of course, if I also include

the pretty important zero to it.

So zero to nine make my
Hindu Arabic numerals.

Similarly, in the Roman system,

they had I, V, X, L, C, D, M.

Now these weren't really
the English alphabets

that they used, right?

We just picked the English alphabets that

looked closest to the
symbols that they were using.

They were using some symbol
that looked like this,

like a stick basically,

just a vertical stick to denote one

and then they had a symbol V for five,

X for 10, L for 50, and C for 100.

And that's, this is probably
enough if you know these

and if you're interested then there's D

and this L-C-D always sticks out to me.

D is for 500 and M is for thousand.

Now you can notice that using these

we don't yet know how to form,

how to read or write Roman numerals.

All we now know is that these
are the digits that they use.

So, in the Hindu Arabic system,

maybe I should write Hindu Arabic way out,

Hindu Arabic system,

how do we write numbers using these.

If I want to write 120 then I would take

a hundred in my third
digit, as my third digit,

then put my two 10s and then zero ones.

Then I would call this 120.

So I'm using the place value system

which you're probably
familiar with right now,

the place value system.

The Roman numerals did not
have a place value system

and they did not even have a
specific alphabet for zero.

So there is no zero as you can see here.

So they were quite a bit different

from our Hindu Arabic numerals,

but the interesting thing here is to learn

how do we read and write in them

and it's not really to
remember to do that,

you probably won't be doing it too often.

It's just a fun exercise
that we're going to be doing

to our own brains.