Calculating profit with addition and subtraction | 4th grade math (TX TEKS) | Khan Academy

- [Instructor] We're told

that Lily bought a backpack for $26.45

and spent $18.97 on
accessories to decorate it.

She sold the decorated
backpack for $67.56.

What was Lily's total profit

from selling the custom backpack?

All right, pause this
video and have a go at that

before we do this together.

Okay, well let's just first
think about what profit is.

So profit, you can view it as
money earned, money earned,

minus money spent, minus money spent,

is going to be equal to your profit.

Let me do this another color.

So this is going to be
equal to your profit.

So what you need to do is just figure out

what's the money earned

and then what's the money
spent and then subtract them.

So what's the money earned?

How much did she bring in?

Well, the money earned in this situation

is going to be what she
sold the backpack for.

That's what she got.

So the money earned is this
piece right over here, $67.56.

That's the money earned.

So we have $67.56,

and then we're going to subtract
from that the money spent.

Now what was the money spent?

Well, she spent some money twice.

She bought a backpack for $26.45

and then she spent another $18.97

on accessories to decorate it.

So the total money spent...

I'll do it over here.

Money spent, the total...

I mean, I'll just write it here.

Let me just write it.

So money spent, money
spent, is equal to $26.45.

Actually, let me do it over here

'cause actually I just wanna line them up

so I can just do the computation.

So it's $26.45 plus $18.97.

Let's add these together.

We'll go to the pennies
or the hundredths place.

Five plus seven is 12.

Go at the two there, regroup that one.

And now we have one plus four plus nine

is going to get us to 14.

We could put the four there.

Regroup that one. That's a whole.

Put the decimal there.

One plus six plus eight, that's seven.

Plus eight, which is 15.

Regroup the one.

One plus two plus one is 45

or it's 40 or four.

And so this is $45.42
cents is what she spent.

So money earned, that's
what she brought in,

minus what spent is $45.42.

And so now we just have
to do this subtraction

to get our profit.

And actually let me do that over here.

So if I have 60...

That's too light of a color.

If I have $67.56

and from that I am subtracting $45.42.

So let's see if I have six minus...

I'll put the decimal here.

Six minus two is going to be four.

Five minus four is one.

Seven minus five is two.

Six minus four is two.

So we get to $22.14 of profit.

Let's do one more example here.

So let me delete this

and now let me bring up another problem.

And move it up so we can see it properly.

And so here we are told that Maya spent

$9.24 on ingredients to bake two cakes.

She sold one cake for $13.29
and the other for $17.45.

What was the total profit
from selling the two cakes?

Again, you could pause this
video, have a go at that.

Well, once again, it's money earned

minus money spent.

So what's the money earned?

So the money earned here is...

So this is how much she spent and then,

but what she sold it for,

that's the money that she got.

So she sold one cake for 13.29

and the other for 17.45.

So let's see.

If we add the both of these.

That's her total money earned.

So nine plus five is 14.

One plus two plus four is seven.

Three plus seven is 10.

Regroup that one.

One plus one plus one is three.

So total money earned is $30.74

and from that we're going
to subtract the money spent,

minus $9.24.

Let me do that in another color.

So minus $9.24, which is
that right over there.

And we could do this separately,

or you might be able
to do this in your head

because if you have 74
cents minus 24 cents,

that's going to give you 50 cents.

And then $30 minus $9 is $21, is 21.50.

You could also write it out
the way we did the last one

where you just put the
9,24, line up the decimals

and subtract accordingly.

But that's her total profit
from selling the two cakes.

And we're done.