Mulitplyling Decimals 3

U03_L2_T2_we5 Mulitplyling Decimals 3

What is the cost of 14.6 gallons
of gasoline at $2.70

per gallon?

So we have 14.6 gallons,
and each gallon's

going to cost $2.70.

Or we can even view $2.70
as 2.7 dollars.

Let's just multiply times 2.7.

It makes things a little
bit simpler.

I think you'll appreciate $2.70
is the same thing as 2.7

dollars per gallon.

So let's multiply this out.

So first we have, and just as a
reminder, when you multiply

decimals, you just have to treat
the numbers like whole

numbers and then worry about
the decimals later.

So right now, we can just view
this as 146 times 27, and then

we'll worry about
the decimals.

So first we have
a 7 times a 6.

7 times 6 is 42.

Regroup the 4.

7 times 4 is 28, plus 4 is 32.

Regroup the 3.

7 times 1 is 7, plus 3 is 10.

So we get 7 times
146 is 1,022.

Now we're going to
deal with this 2.

But this 2, at least before we
consider the decimal, is

really a 20.

So we're going to
put a 0 here.

We're doing it exactly the same
way we do a traditional

multiplication problem.

We're ignoring the
decimals for now.

2 times 6 is 12.

Carry the 1, or regroup the 1.

We can ignore these
guys right now.

2 times 4 is 8, plus 1 is 9.

2 times 1 is 2, and
now we can add.

And we get 2 plus 0 is 2.

2 plus 2 is 4.

0 plus 9 is 9.

1 plus 2 is 3.

Now we've figured out what
146 times 27 is.

It's 3,942.

But this wasn't 146 times 27.

It was 14.6 times 2.7.

So now we have to worry
about the decimals.

We just count how many numbers
are sitting behind decimals.

We have one right there and
a second one right there.

So our product has to have
two numbers to the

right of the decimal.

So one, two, stick it
right over there.

So for 14.6 gallons of gas at
$2.70 per gallon, it's going

to cost $39.42.