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Current time:0:00Total duration:5:37

CC Math: 4.MD.A.2

- [Instructor] Brooklyn
purchased three pounds of pasta and 12 ounces of cheese to
make macaroni and cheese. What is the total weight, in ounces, total weight in ounces, of the pasta and cheese combined? So they give us the weight
of the pasta in pounds, and they give us the weight
of the cheese in ounces, and we want to add the total weight, but they have to all be in ounces. So let's first, let's first convert these
three pounds of pasta into a certain amount of
ounces of ounce, of pasta. So we already know that one
pound is equal to 16 ounces. They tell us that. So what would three pounds be? So, if I had three pounds, how many ounces would that be? I encourage you to pause the
video and think about it. Well, let's see, if you're
having three times the pounds, you're also going to have
three times the ounces. So, if one pound is 16 ounces,
if you have three times as many pounds, you're
gonna have three times as many ounces. So 16 times three is 48, 48 ounces. So Brooklyn, the three pounds
of pasta that she purchased, that can also be viewed as 48 ounces. 48 ounces of pasta. So she has 48 ounces of pasta, and 12 ounces of cheese. So what is the total weight,
in ounces, of them combined? Well it's going to be 48 ounces 48 ounces plus the 12 ounces of cheese. 48 ounces of pasta plus
12 ounces of cheese, give us a total of 60
ounces of pasta and cheese, combined. Let's do another example, with other units. So we are told, David is making a wall out of bricks. Each brick is 2/3 of a foot long. Each brick is 2/3 of a foot long. There are 20 bricks lined up
end to end to make the wall. What is the total length
of the wall in inches? We've got to pay attention to the units. So they give us the length
of each brick in feet. So, we know that each brick here, let me draw a brick. The length here is 2/3 of a foot. 2/3 of a foot. So what would this length be in inches? Well, once again, we can look
at the conversion between foot and inches. If I go from one foot to 2/3 of a foot, well I've multiplied by 2/3. So, if one foot is 12 inches,
and if I want to know how many inches 2/3 inches, or 2/3 of a foot is in inches, well, I would multiply by 2/3 again. In either case, you could
view this as multiplying both sides of this conversion, by 2/3. And so, 2/3 of a foot
is 2/3 times 12 inches. And so 12 times two over three, that would be 24 over three. So this is going to be
equal to 24 over three inches. I'll just write I-N for
short, right over here. 24 over three, which is
equal to eight inches. So each brick is, either you
could view it as 2/3 of a foot long or you could view it as eight inches. Eight inches long. And there are 20 bricks lined up end to end to make the wall. So what is the total length
of the wall in inches? Well, it's going to be eight brick, each brick is eight inches, times 20. Times 20. And eight times two is 16, so eight times 20 is 160 inches. Let's do one more of these. And this time, let's
deal with some volume. So this says, Blanca buys
two gallons of green paint. She uses five quarts to
paint her front porch and 0.5 quarts to paint the front porch swing. How may quarts of paint
does Blanca have left? So we're given the
original amount in gallons, but we want to know how
many quarts she has left. So let's convert the amount
she originally has into quarts. So they tell us one gallon
is equal to four quarts. So two gallons, two gallons is going to be equal to two gallons is going to be twice as many quarts, is gonna be eight quarts. So that's what she starts with. And one way to think about this, I just took this conversion, well if I'm a have twice as many gallons, then I'm gonna have twice as many quarts, if I want to express
that volume in quarts. So, one way of thinking about it, she starts with eight quarts. She starts with eight quarts. Eight quarts. She uses five quarts to
paint her front porch. So minus five quarts, on the front porch, is what she used. And she used .5 quarts
to paint the porch swing. So minus 0.5 quarts. That looks like a "g." 0.5 quarts. Well, what is that going to be? Well, eight minus five is three, minus .5 is 2.5. So she is going to be
left with 2.5 quarts. And we have answered the question in terms of the units they care about. In terms of quarts.