Input & output tables: identifying the rule | 4th grade math (TX TEKS) | Khan Academy

- [Instructor] The table
shows the relationship

between input and output numbers.

So they're saying that when I put 27 in,

I guess you could say to this table,

or we're going to be
doing something with it,

so this is a number we're
gonna do something with.

And after we do that something,
we output nine, interesting,

we input 15, we output
five, when we input six,

we output two.

Which rule can we use to find the output

when given the input?

Pause this video and have a go at that.

All right, now let's work
through this right over here.

There's a bunch of ways
we could think about it,

but the same rule's gotta
work for all of these inputs

and outputs.

So this first one says we subtract 18,

so when we look at this
first choice, if we take 27,

and if we were to subtract 18,

it does indeed look like that, well,

that would be equal to
nine, so that one works.

But if I took 15 and
I were to subtract 18,

I definitely don't get five.

So I don't even have to
go to that third row here,

I can rule out choice A, so
let me rule that one out.

Let's see subtracting nine.

Well, that one doesn't work even

on the first one right over
here, if I do 27 minus nine,

it doesn't equal nine, it equals 18.

It actually doesn't work for any of these,

so we could rule that one out as well.

Divide by three, this one's interesting.

27 divided by three is equal to nine.

15 divided by three is equal
to five, it's looking good.

Six divided by three is equal to two, yep.

You give me any input, I divide by three,

it looks like that's the
output you're going to get.

So I like this choice.

Five, this last one's not going to work,

but we can verify that, 27 divided by five

is definitely not nine, 15 divided by five

is definitely not five,
and six divided by five

is definitely not two, so that
one's definitely not right.