Calculating profit with multiplication | 4th grade math (TX TEKS) | Khan Academy

- [Instructor] We're told
that Sarah spent $79.98

on materials to create custom candles.

She sold 12 candles for $14 each.

What was Sarah's profit
from the candle sales?

So pause this video,

have a go at that before
we do this together.

So let's just remind
ourselves what profit is.

Profit is going to be equal

to the money that you earn,

maybe I'll write that in green

'cause that's a good thing,

money that you earn,

but you probably spent some
money to get that money,

minus the money that you spent.

So let's think about the
money that Sarah earned here.

Well, we see here that she sold 12 candles

for $14 each.

So the money that she earned
is going to be 12 times $14.

So there's several ways we could do that,

but let's just do 12 times 14.

We could say 4 times 12.

Well, I'll just do it the standard way

just to not confuse you a little bit.

4 times 2 is 8,

4 times 1, it's really 4 times 10,

is 4 or 40.

Since we're looking at the place values,

we'll put a 0 here

since we're gonna be
multiplying everything

times this one now.

And then 1 times 2 is 2,

1 times 1 is 1.

Or another way to think about that,

4 times 12 is 48

and 10 times 12 is 120.

And now we can add all of this together,

8 plus 0 is 8,

4 plus 2 is 6,

and then we have this 1 here.

So the total money earned is $168.

And what is the money spent?

Well, it says that Sarah spent $79.98,

so minus 79.98.

If I figure this out, I know
what the total profit is.

Some of you might be able
to do this in your head,

but I will just break this down

just to make this a little
bit more straightforward.

So we are going to have,
let me do that green color,

168.00 minus

- 79.98.

And what is this going to be equal to?

Well, I'm gonna have to do a little bit

of regrouping over here.

And so I am going to,

well, even here, this
8 is less than this 9,

the 6 is less than the 7.

So let's take this 100 and
put it into the tens place,

so it'd be 10 tens.

So if we add those 10 tens

to the 6 tens that are already there,

we get 16 tens.

And now I can take one of those 16 tens,

so I have 15 tens,

and turn that into 10 ones,

so now I have 18 ones.

And then I can take one of those 18 ones

so now I have 17 ones

and turn it into 10 tenths.

And then I can take
one of those 10 tenths,

so now I have 9 tenths

and turn it into 10 hundredths.

And now I'm ready to subtract,

10 hundredths minus 8
hundredths is 2 hundredths.

Nine hundredths..

Sorry, 9 tenths minus
9 tenths is no tenths.

And then 17 ones minus 9 ones is 8.

And then 15 tens minus 7 tens

is going to be equal to

15 tens minus 7 tens

is also going to be equal to 8.

And so then we have...

Let's see, did I do all that right?

Okay, there we go,

we have $88.02.

And I like to just double check that.

If I were to subtracting $80,

so if I just add 2 cents to this,

if I were to subtract $80 from this,

I would get straight to $88,

but I'm subtracting 2
cents less than that,

so it makes sense that I got to $88.02.

Let's do another example. These are fun.

So here we are told

that Elena bought 15 vases for $12 each.

She cleaned and polished the vases,

then she sold them for a total of $279.67.

What was Elena's total
profit from the vase sales?

Again, pause the video,

try to figure this out
before we do this together.

Well, just remember,

profit is money earned minus money sold.

So what's the money earned?

Well, that's what she sold them for.

She sold them for a
total of $279.67 cents,

$279.67.

And from that we need to
subtract the money spent.

Some money spent, what's the money spent?

Well, she bought 15 vases for $12 each,

so let's multiply 15 times 12.

2 times 15 is 30,

and then 10 times 15 is 150,

we're going to get to 180.

So you have $279.67

minus the total amount she spent,

which is $180.

And so this is going to be equal to,

some of you...

I'll do it both ways.

Well, actually, it gets
a little complicated

so I'll just do the subtraction

so we're gonna have $279.67

minus $180.

That's going to give us our total profit.

7 minus 0 is 7,

6 minus 0 is 6,

9 minus 0 is 9.

I could just think of 27 minus
18 is 9 and put that here

or I could do a little bit of regrouping,

take one of these hundreds

and make that into 10 tens.

So 17 minus 8 is 9,

and then I have no hundreds left,

so I get a total profit

of $99.67.

Another way that you could just make sure

you're in the right ballpark.

If this was $280,

so just a little bit more minus $180,

that would've been $100.

But we are just a little bit less,

we're 33 cents less than that,

and so it makes sense that we're 33 cents

less than $100 right over here.