Mike built a rectangular dog

pen that is 21 feet long, and it has a

perimeter of 78 feet. What is the width

of Mike’s dog pen? So let’s try to

draw this dog pen. So it’s going to

have some width, and I’ll just label

that as the width. And it’s going to have

a length of 21 feet. So this distance right over

here is going to be 21, and of course, this is as well. It’s a rectangle,

so this is also going to be a distance of 21. And of course, this

distance down here is also going to be the width. Now, how do you calculate

the perimeter of this? They tell us that the

perimeter is 78 feet, but how do we calculate

the perimeter using this information? Well, the perimeter

is just the sum of these two widths

and these two lengths. So the perimeter is going to

be the width plus the width plus the two lengths,

plus 21 plus 21. This will give us

the distance if we go around this

rectangular dog pen. And they tell us that this thing

needs to be equal to 78 feet. Let me do the same color. Now, we could simplify

this expression on the left hand

side a little bit. We know that the width plus the

width plus the sum of the two lengths– which are

both the same– plus 42 is going to equal 78. So what must the width

plus the width be equal to? So, I have something–

I have this thing plus 42 is equal to 78. So if I have something

plus 42 is equal to 78, that means that this

something must be 78 minus 42. So let’s write that down. Width plus width is going

to be equal to 78 minus 42, which is– I’ll do it in a

new color– 78 minus 42 is 36. And you can verify this. If this thing right over

here is equal to 36, if the sum of my two

widths– or essentially this is 2 times the width. If 2 times the width is 36,

then width plus width is 36. Then this right over here is 36. 36 plus 42 is

indeed equal to 78. So we figure out a width so that

if I add the width to itself, I get 36, because when we

add those two, you get 36, plus 21 plus 21 is equal to 78. So what number plus itself

is going to be equal to 36? Another way to rewrite this

is a number plus itself is the same thing as

2 times that number. So 2 times the width is

going to be equal to 36. And later on when we learn

algebra in a little bit more detail, you’ll see that

essentially what we’re doing is actually algebra, but it

just comes out of common sense, out of logic. So if I say 2 times some

value is equal to 36, what is that value going to be? Well, 2 times 18 is 36, so

the width is equal to 18. And you might say well,

how did I figure out that the width is equal to 18? Well, there’s a couple of

ways to think about it. If 2 times the width

is equal to 36, then the width must be

equal to 36 divided by 2, must be equal to 36 over 2,

which would also get you 18. So there’s a lot of

ways to think about it, and later on when we learn

algebra in a little bit more details, things like this

will seem even more obvious. But I just wanted to show

you that you can actually reason this through just with

what we know about perimeter.

find the length given perimeter and width

find the length given perimeter and width

π©

Really explanative πππππππππππ

I can't understand >_<>_<

Thanks,it help me a lot

Thanks bro I learnt how to solve

Formula??

ππ»

h e l p π

Mojja

how do i find the length when only given the width and not the perimeter or area

Wow, you guys are doing this 100% for free. RESPECT

How to find the width without any length and with perimeter

I donβt understand π (>_<)

Omg I have this type of math problem in collegeπ©π

Thanks for this I understood everything ππ

Thank you so much for this video! My professor never explains as detailed as you and gives a difficult way to solve it

Basically:

You have your lengths already. Add them together and subtract it from the perimeter (ex: 1+1=2 6-2=4). Now, divide the remainder by two and that is your width (ex: 4Γ·2=2).

Thank you