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## Geometry (all content)

### Course: Geometry (all content) > Unit 7

Lesson 3: Perimeter- Perimeter: introduction
- Perimeter of a shape
- Find perimeter by counting unit squares
- Find perimeter by counting units
- Finding perimeter when a side length is missing
- Find perimeter when given side lengths
- Finding missing side length when given perimeter
- Find a missing side length when given perimeter
- Perimeter & area
- Perimeter and unit conversion
- Applying the metric system to perimeter
- Perimeter review

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# Applying the metric system to perimeter

Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

- How do you convert liters to milliters(1 vote)
- that depends on the value there is a jump system if it takes two jumps it is 100 and one so 10 by counting the 0's and putting the decimal(1 vote)

- I thought the width is the SHORT side of a rectangle and the length is the LOOONG side of a rectangle.Am I wrong??(3 votes)
- It depends on your point of view. When defining a square or 3-dimensional object like a box you just give the measure 6x12 or 6x12x7. The width could either be 6 or 12, if it is 6, the length is automatically 12 and visa versa. If you are in front of the box, most people would say the width is the side on your front and the length on the right and the left. If you turn the box 90 degrees, the side on your front is the width where it was previously the length. So it doesn't matter as long as the size of the object stays the same and correct.(2 votes)

- at4:50u have subtracted 320 with -320 then again u subtracted on the right hand side, 720 with -320, i understand if u are subtracting the left hand side with something to have to subtract it with the right hand side too, but i don't understand why to don't subtract 2w with -320 ??(1 vote)
- Fahad,

You are trying to solve for w. To do this, you want to end up with the w all by itself on one side of the equation.

Sal had

2w + 320 = 720 So he subtracted 320 from boht sides.

2w + 320 - 320 = 720 - 320 so

2w + 0 = 720 - 320 so

2w = 720-320 so

2w = 400 Now you still want to get the w by itself, so you divide both sided by 2

2w/2 = 400/2 and 2/2 = 1 so

1w = 400 and 1w is just w so

w=400/2 so you have w all by itsefl on one side Now divide 400 by 2

w=200 so now you know that w is 200.

If instead you had subtracted 2w from both sides, the w would have ended up on the same side with the other numbers instead of by itself.

I hope that helps make it click for you.(3 votes)

- isn't the length the longer side and the width the shorter side(1 vote)
- 2,500 mg= 2.500g ?(1 vote)
- What place in this world can have their temp. F and C equal?(1 vote)
- The only place might be -40 degrees cold must be Antarctica(1 vote)

- what is the metric system i really dont understand it(1 vote)
- The metric system is one of the major measuring systems used by the world today, especially in science. If you want a full history of the metric system, the wikipedia page is pretty good.

http://en.wikipedia.org/wiki/History_of_the_metric_system(1 vote)

- whats the area of a polygon?(1 vote)
- Is this video not the same as the one entitled Perimeter and unit conversion that is the lesson before this in Ratios, Proportions, Units and Rates in Pre-Algebra? Although different video but it covers same exact problem on perimeter with same values.(1 vote)
- Does The U.K only follow The Imperial system?(1 vote)
- The UK uses both, although there are certain measurements that must be given in imperial units by law. For example, beer etc. in pubs must be sold by the pint or half pint and road distances must be given in miles, yards and feet.

Most other commodities are sold with both imperial and metric measures indicated, although there is a tendency for supermarkets and very large organizations to sell only in metric. Small businesses and market stalls tend to use mainly imperial as survey after survey has shown that many shoppers understand imperial units better for everyday purposes such as buying fruit and vegetables. This is despite decades of schools teaching almost exclusively in metric, and pressure from the European Union.

Fuel is usually sold in metric.

The weather forecast is usually gives the temperature in Celsius.

Informational pamphlets such as property details usually use dual marking.

Goods brochures usually use dual marking.

Milk is usually sold by the pint or the quart.

Horseracing still uses the Furlong. And a cricket pitch is one chain in length (22 yards).

A lot of goods come in an "Imperial" sized container, but marked in metric, e.g. 454g (1 lb), or 568ml (1 pint). Everyone refers to it as a "pint" or a "pound" however.

Most U.K. citizens, if asked their height or weight, would tell you in Imperial.

The U.K. also uses some Imperial measures that are not used in the U.S. For example, hundredweights (112lbs) and stones (14lbs).(1 vote)

## Video transcript

The perimeter of a rectangular
fence measures 0.72 kilometers. The length of the fenced
area is 160 meters. What is its width? So we have a rectangular
fence. Let me draw it. So that is a rectangle. You can imagine we're
looking from above. This line is the top
of the fence. And if you take its perimeter,
the perimeter is the distance around the fence. If you take this distance plus
this distance plus that distance plus that distance,
it's going to be 0.72 kilometers. That's the total distance
of all of the sides. Now, the length of the fenced
area is 160 meters. Let's call this the length. So this distance right
here is 160 meters. Since it's a rectangle, that
distance over there is also going to be 160 meters, and we
need to figure out its width. They want us to figure
out the width. The width is this distance right
over here, which is also going to be this distance
right over there. Now, what is the perimeter
of the fence? The perimeter is the sum of this
length plus this length plus that length plus
that length. So the perimeter-- let me write
it in orange-- is going to be equal to w, the width,
plus 160 meters, plus the width, plus 160 meters. And let's assume
w is in meters. So we could add it all up. So if you were to add all of
these up, you'd get a certain number of meters. If you were to add all of these
up, you have a w plus a w, so you'd be 2w, plus-- 160
plus 160 is 320-- so plus 320. And this whole thing
is in meters. We're assuming that
w is in meters. Now, they also told us that the
perimeter of the fence is 0.72 kilometers. So the perimeter-- let me do it
in that same orange color. The perimeter is also equal to
0.72 kilometers, and we can abbreviate that with km. Now, if we wanted to solve an
equation, if we wanted to set this thing equal to the
perimeter they gave us, we have to make sure that the
units are the same. Here it's in meters. Here it's in kilometers. So let's convert this 0.72
kilometers to meters. And the way to do that, we want
the kilometers in the denominator so it cancels out
with the kilometers, and you want meters in the numerator. Now, how many meters
equal a kilometer? Well, it's 1,000 meters
for every 1 kilometer. 1 kilometer is 1,000 meters. Now, if you multiply these
two things, the kilometers cancel out. You're just going to be
left with the meters. And then when you multiply 0.72
times 1,000, you could just first say, OK, let's
take 72 times 1,000. 72 times 1,000 would
be 72 with three zeroes: one, two, three. And then out of the two numbers
that you're taking the product of, we have two
numbers behind the decimal: one, two. So you put two numbers behind
the decimal, one, two, right over there. So 0.72 times 1,000 is 720. And that makes sense. 0.72, it's not quite 1, but
it's getting close to 1, almost 3/4 of a whole, and this
is almost 3/4 of 1,000. So it makes sense. So the perimeter, this
information right here, 0.72 kilometers, is the same
thing as 720 meters. So if you take 2 times the width
in meters, and add that to the combined lengths-- it's
160 and 160, that's 320, and all of this is in meters-- that
is going to be equal to the total perimeter, which
is 720 meters. Now that we have the units
right, we can solve for w, and w will tell us this
width in meters. So 2w plus 320 is
equal to 720. We can subtract 320 from both
sides of this equation. Remember, an equation is saying,
that is equal to that. If we want them both always to
be equal, whatever we do to the left-hand side, we have
to do the right-hand side. So we subtract 320
from both sides. The left-hand side,
that cancels out. That's why we subtracted 320. And you just have left 2 times
the width is equal to 720 minus 320, which is 400. Now you can divide both
sides of this by 2. And then you're left with
the w is equal to 400/2, which is 200. And we said that w was
in meters, so the width is 200 meters. Let's see if it makes sense. 200 plus 200 is 400,
plus 320 is 720. So the total perimeter is 720
meters, which is the exact same thing as 0.72 kilometers.