hi Ashley again today we are going to go a little bit deeper in finding perimeter
you ready let's go so we learned in our last video that perimeter is the
distance all the way around a shape for this second video we're mostly going to
focus on rectangles and we're going to look at some formulas specific to
finding perimeter on a rectangle our first formula here is pretty much the
one we use last time without talking about it so P is for perimeter P is
equal to adding up all of our sides so you see here we have L plus L plus W
plus W L is the length and remember two sides are the length and they are equal
to each other on a rectangle and then the width is also two sides which are
equal let me show you so a rectangle has a length and a width so the two sides
opposite each other our length and the other two are width now there is also
another formula that can be used for perimeter of a rectangle which can be a
little bit simpler to do if you already have been introduced to basic
multiplication so let me show you that 1p perimeter is equal to 2l or 2 times
the length plus 2w 2 times the width so let me show you that so remember our
rectangle has a length both lengths are the same size so we can multiply that
length times 2 and then it has a width and both widths
are the same length or it's same size and we can multiply that by two then we
add both of those answers together and we get our perimeter so our problem here
size find the perimeter of a rectangle with a length of 11 feet and a width of
12 feet now we see our formula listed there below P perimeter is equal to 2l
plus 2w now we can use this formula to solve our problem without having to draw
a picture of our rectangle so what I'm going to do is plug the numbers from the
problem into our formula so my length is 11 I'm going to put that in parenthesis
and I know that needs to be multiplied by 2 now parentheses a number next to it
means multiplied so I can just do that without writing my X for multiplication
now I know I need to add that to 2 times my width which was 12 feet okay when
working with a problem like this that has both multiplication and addition we
always do the multiplication first so 2 times 11 is equal to 22 and 2 times 12
is equal to 24 now I'm going to bring my addition sign down and I just need to
add the 22 and 24 together that gives me a total of can you figure it out 46 46
wet feet my perimeter is equal to 46 feet
always box your answer that makes it your work easier to read okay you ready
for another one this next one will be a bit more challenging
all right let's read this one together if the perimeter of a rectangle is 100
centimeters and three of the sides total 60 centimeters how long is the missing
side hmm did you notice the difference in this question it's telling us what
the perimeter is and it's telling us what three of the sides are 60
centimeters and it wants to know what the missing side is hmm let's plug this
into our formula over here on the right and see what happens okay perimeter is
equal to 100 centimeters right and what was it three of these sides go together
to make 60 so remember total means addition so three of these added
together is 60 right now I still have this missing length right W there is not
filled in and that's what we need to know hmm well we need to get this W by
itself so that we can figure out what it is we need to do the opposite of
addition so what we're going to do here is we need to take this 60 away okay if
we take the 60 away here I can mark that out because 60 minus 60 is zero right so
I'm going to take it away here as well 100 minus 60 what is 100 minus 60 40
okay and I can bring this equal sign down and my W down so W is equal to 40
that means our missing side here is 40 40 centimeters so the answer to this
problem our missing side is 40 centimeters oh did you get all that
please go back and watch this problem again if you need some help so now that
we've done that one let's learn the formula for perimeter of a square okay
square similar to a rectangle we add up all the sides but since all the sides
are equal on a square we could just multiply it by 4 because it has four
equal sides so the perimeter of a square we can just multiply it by four so P for
perimeter is equal to 4s meaning four times this length of a side okay now
let's try this out our first problem here says what is the perimeter of a
square with a side length of 4 centimeters well using our formula all
we need to do is multiply 4 centimeters by four because there are four sides
equaling four centimeters each so four times four is equal to 16 centimeters
and that is our perimeter perimeter equals 16 centimeters let's try it one
more if the perimeter of a square is 40 inches what is the length of each side
hmm okay again like with our tough rectangle
one we are given the perimeter and we need to know what the length of the side
is I am going to plug in these numbers into our formula we have 40 inches is
equal to four times the length of our side and that's what we're trying to
figure out well four times the length of our side what we need to do is the
opposite of multiplication which is what you say division if you did that's right
so to find our missing number what we need to do is divide we are going to
take our perimeter and divide it by four so 40 divided by four is equal to ten
you got it so our side here each side on this square is equal to ten inches box
our answer and that's it great job be sure to go practice what
you've learned with our online games and quizzes and remember to always be clever