Perimeter Patterns

Geometry Level 1

By tracing the edges, we can calculate that the perimeter of figure 1 is 4 units, and the perimeter of figure 2 is 12 units. What is the perimeter of figure 3?

16 28 12 20

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22 solutions

Abhishek Jha
Apr 17, 2014

When a new box is added at one of the "ends" of figure 2, it adds exactly 2 new edges:

Since 4 boxes are added, the perimeter change is +8, so 12 + 8 = 20. 12+8=20.

We can set up a function to calculate the perimeter. Let the figure no. be x x , then ---->

f ( x ) = 4 + 8 ( x 1 ) f(x)=4+8(x-1) where f ( x ) = f(x)= Perimeter of Figure x x .

Prasun Biswas - 7 years, 1 month ago

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Wow! so cute equation

Prokash Shakkhar - 4 years, 5 months ago

Nice logic ;-)

Ojasee Duble - 4 years, 4 months ago

Nice! I did it the same way :-)

Malin de Koning - 3 years, 5 months ago

Whaaaaaaaaaaaaaaaaaaaaaaaat

GHULAM MAHBOOB AHMAD SIDDIQUE - 2 years, 2 months ago

i just knew that it has the same perimeter as a square of the same size.

andrew Tolley - 1 year, 12 months ago

It actually helps on what you are doing

Maritza Antonio - 1 year, 2 months ago

It's hard but it's helps

Qwerty Anonymous - 11 months ago

Excellent solution. We should say that when a box is added to one of the four ends, it adds exactly 2 units, (not edges).

Shannon Sims - 9 months, 1 week ago
Chamelean Brown
Apr 17, 2014

Number of boxes 'n' P=2n+2

This formula feels so quick! :-D

Ojasee Duble - 4 years, 4 months ago

Your solution is the best. You use explicit formula. How did you come to this solution?

Vitaliy Soroka - 3 years, 9 months ago
Pranav Adatia
Apr 21, 2014

We can simply count the each side of a square which faces the outer side, and find 20 of them:

well if they wrote it "by counting sides of each square..." Instead of "by counting edges"...

Nikola Abramovic - 5 years, 5 months ago
Kaif Ahsan
Apr 17, 2014

Focus on the ratio here. For one square the perimeter was 4. For another 4 squares the perimeter raised to 12. So, the perimeter raises 8 units for 4 square. So, the perimeter of fig. 3 will be 12 + 8 units=20 units.

Edwin Gray
Apr 17, 2019

The perimeter is 2(n + 1), where n is the number of squares present.

Ramji Varadarajan
Apr 17, 2014

By counting all the outer sides of the figure, taking 1 side=1 unit, we get its perimeter as 20.

F i g . 1 : P = 4 ( 4 1 ) Fig.1:P=4\Longrightarrow (4\cdot 1)

F i g . 2 : P = 12 ( 4 3 ) Fig.2:P=12\Longrightarrow (4\cdot 3)

F i g . 3 : P = 4 ( 4 5 ) Fig.3:P=4\Longrightarrow (4\cdot 5)

\vdots

Having noticed this:

n = n u m b e r n=number o f of a r r o w s , arrows, f ( n ) = p e r i m e t e r f(n)=perimeter

Then:

f ( n ) = 4 n \boxed{f(n)=4n}

Annie Li
Mar 20, 2017

The simple way to do this is simply counting the edges

That is better

Marion Akello - 3 years, 12 months ago

Or count the edges on one of the four parts jutting out, then multiply by 4

John Hopkins - 2 years, 10 months ago
Mari B
Jan 2, 2016

perimeter figure 1 = 1*4

figure 2 = 3*4

figure 3 = 5*4

y = (2x-1)4

or you could just count the number of edges sticking out on one of them sticks and times it by 4. 1 4 3 4 5*4

That is a nice solution Marion Edith from mpesa foundation academy

Marion Akello - 3 years, 10 months ago
Ken Graf
Apr 17, 2014

4 sides with 5 units each. 4 x 5 = 20

it is also 12 unit peremeter

Asif Dogar Asif Dogar - 7 years, 1 month ago
Vishakha Sharma
Apr 17, 2014

4 boxes have 3 sides, and 4 have 2 sides. Therefore (3 x 4) + (2 x 4) = 20

Different approach to

Zakaria Ameen - 7 years, 1 month ago
Kaloyan Todorov
Feb 18, 2020

We can find the solution with this formula P=n.4-(n-1).2

where n is the number of squares :)

Kaloyan Todorov - 1 year, 3 months ago
Orion Rhoades
Feb 14, 2018

For figure n, it simplifies down to p ( n ) = 4 ( 2 n 1 ) p(n)=4*(2n-1) . Here, the value is simply p ( 3 ) = 4 ( 2 ( 3 ) 1 ) p(3)=4*(2(3)-1) , which is 20.

Anshika Sinha
Feb 11, 2018

In fig. 1 the unit of edge is 4unit and the fig.2 the unit of edge is 8unit.. It means that when the blocks are increased the no. Will also be increased. It increases by multiple of 4 b/w the 2 gaping..ex.4×3=12,4×5=20 so total block of perimeter is 4 +8+8=20 i.e p= 2n+2

Marion Akello
Jun 17, 2017

Since the first figure has 4 units, the second one has12 units, this means that they were getting the perimeter of the figures and this meant that one side of the square has 1 unit. If you count the sides in figure 3 you will be able to find out that they are 20 which means you don't count those that are attached on the sides.Marion Edith from Mpesa foundation academy.

   AT LAST  YOU GET YOUR ANSWER AS=20

Nic e solution

Marion Akello - 3 years, 10 months ago
Srihari Vishnu
Jun 15, 2014

Find the length from 1 end to other and multiply into 4

Oliver Daniel
Apr 19, 2014

Every time a box is added it increases the length of each arm by one unit or the perimeter increases by 2 units. For four boxes it increases by 8 units and so the answer is 12+8=20.

4,12,20

Felipe Bz
Apr 17, 2014

Each side block is of 5 units ,so four sides will have 20 Ans

Aditya Jha
Apr 17, 2014

every time there will be increment of 8 units (3*4-4)

Shahid Qureshi
Apr 17, 2014

Take Fig. 1. The Square is having 4-Sides and each side is 1-Unit in length and so the Periphery of square is 4-Units. In big Cross, 9 Squares are included so the total Periphery of 9 squares will be 36 Units. But in the Fig. 3, there are 16 Sides of 9 squares which are not Part of Periphery, so 36 - 16 = 20 sides, which are making the Periphery of Fig. 3. Thus Periphery will be 20 Units.

we can't count like this 1 2 3 4 . . . . . . . . . we need even numbers. 2 4 6 8 . . . . . . . . . . so on. and if we do this y = d. then we could just make 2 again. crazy mathimatics. right! but its y thats 2.

Am Kemplin - 1 month, 2 weeks ago

24681012141820

Am Kemplin - 1 month, 2 weeks ago
Aashish Patel
Apr 17, 2014

It is given that the square one has a perimeter of 4 units.This means that each side of the square measures 1 unit.So in the last figure we just have to count the number of edges of each square.

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