Question

Figures I and II are similar pentagons. Find the Perimeter of pentagon II.

Answer 1

@paul1231

Answer 2

the two pentagons are similar
what do you think that means?

Answer 3

I dont know how to start this problem.

Answer 4

the ratio of their perimeters is equal to the ratio of their corresponding side lengths

Answer 5

How do i find any of their side lengths though?

Answer 6

@heather040200

Answer 7

we have two figures A and B
if A is similar to B
it means that if we multiply A with some number x
we will get B
so Ax =B
(THEY ARE IN RATIO)
what does this mean to us
side(A) * x = side(B)
where side(A) means side of A

perimeter(A)*x = perimeter(B)

area of(A)*x = area(B)

i hope you get the point

Answer 8

it is given that the
Area of I = 43 cm^2
Area of II = 387 cm^2

but they are similar so find their ratio
Area II/Area I = 387/43 = 9

the perimeter of II would be 3*25 = 75 cm
and the side length of II would be 75/5 = 15cm

Answer 9

We know that if you find the ratio of the areas and take the square root, you will have the ratio of the perimeters
So find the ratio of the areas: 387/43

Answer 10

dammit heather why are you so hot ? :X

Answer 11

why 3 X 25?

Answer 12

because the units of area is cm^2
and the units of perimeter is cm

Answer 13

9cm^2 = 3cm

you cannot really multiply 25cm with 9cm^2 because their units are different
so you have to convert 9cm^2 to 3cm before you can multiply them

think about adding 10grams to 15 meters
it does not make sense does it

Answer 14

oh yeah i think i get it so i can say.... perimeter II= 3/1 X 25? why am i multiplying 25 though... where did that come from?

Answer 15

25 is the perimeter of the small one you are trying to find the big one

Answer 16

yeah but why multiply the perimeter of the small one by the ratio of the areas of the two? What exactly is the formula?

Answer 17

there is no formula
the two objects are similar
which means they are in ratio
so their areas are in ratio
and their peremeters are in ratio
and their sides aswell

Answer 18

bcuz the ratio tells you how big they are to each other they are 3:1 that means the bigger one is 3 times bigger then the smaller one so the perimeter of the big one is going to be 3 times bigger then the small one

Answer 19

does this make sense... Perimeter of II/Perimeter of I= 3/1 therefore, Perimeter of II= 3(25)=75 cm.

Answer 20

looks good to me :)

Answer 21

Thanks for the help guys!

Answer 22

this is how you answer it

given :
Ar(I) = 43cm^2
Ar(II) = 387cm^2
Perimeter(I) =25cm^2

to find:
Perimeter(II)

Since fig.I and fig.2 are similar it implies that the two objects are in ratio.

Ar(II)/Ar(I) = 387cm^2/43cm^2 = 9cm^2
the magnitude of their ratio = 9 cm^2
or sqrt(9cm^2) = 3cm

upon multiplying Perimeter(I) with 3
we get, 25*3 = 75cm^2
which is the perimeter of fig.II

Answer 23

No problem :)

Answer 24

looks good

Answer 25

well that will also work :X