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Math Puzzle [num18]

Blogs > evanthebouncy!
Post a Reply
evanthebouncy!
Profile Blog Joined June 2006
United States12815 Posts
Last Edited: 2011-02-09 11:14:08
February 09 2011 10:06 GMT
#1
Dear readers!! It has been a long time since I've posted one of these! This one is very cute so hear me out :3

You have a square pizza, and per usual, pizza has crust on the outer perimeter. To simplify, you can think of the crust have no width but only length (so the bend on the corner isn't really a concern to us). Your job is to cut the pizza into 5 equal parts, such that each part has the same amount of area AND the same amount of crust.

In a formal way: Divide a square (with boundary) into 5 equal area parts such that each part contains the same amount of the original boundary. And prove why your method work, of course.


Which tools can we use ? Is that supposed to be a compass and straightedge construction ?

Answer: Nah, that would be more restriction than nessesary.

As usual, put answer in spoilers, and have fun!

edit:
If you have some half-formed idea just post them anyways to keep the thread going, and discussions can be very insightful.

Life is run, it is dance, it is fast, passionate and BAM!, you dance and sing and booze while you can for now is the time and time is mine. Smile and laugh when still can for now is the time and soon you die!
kOre
Profile Blog Joined April 2009
Canada3642 Posts
February 09 2011 10:29 GMT
#2
+ Show Spoiler +
Cut at every 72 degree? Pretty much splitting the pizza into 5 equal parts and they should have equal crust amounts?
http://www.starcraftmecca.net - Founder
evanthebouncy!
Profile Blog Joined June 2006
United States12815 Posts
February 09 2011 10:31 GMT
#3
On February 09 2011 19:29 kOre wrote:
+ Show Spoiler +
Cut at every 72 degree? Pretty much splitting the pizza into 5 equal parts and they should have equal crust amounts?
A: I bolded a letter my question for you

Life is run, it is dance, it is fast, passionate and BAM!, you dance and sing and booze while you can for now is the time and time is mine. Smile and laugh when still can for now is the time and soon you die!
kOre
Profile Blog Joined April 2009
Canada3642 Posts
Last Edited: 2011-02-09 10:33:14
February 09 2011 10:32 GMT
#4
+ Show Spoiler +
Like this except actually at every 72 degree angle.

[image loading]
http://www.starcraftmecca.net - Founder
RisingTide
Profile Joined December 2008
Australia769 Posts
Last Edited: 2011-02-09 10:50:51
February 09 2011 10:33 GMT
#5
Got it but I have no idea how to represent it :D

Nvm: got an idea.
+ Show Spoiler +

Cheater
+ Show Spoiler +

[image loading]


Basically consider it a 10x10 grid, and divide into sections with a perimeter 8 and area 20.

kaleidoscope
Profile Blog Joined December 2008
Singapore2887 Posts
February 09 2011 10:35 GMT
#6
On February 09 2011 19:29 kOre wrote:
+ Show Spoiler +
Cut at every 72 degree? Pretty much splitting the pizza into 5 equal parts and they should have equal crust amounts?


+ Show Spoiler +
the corner (crust)will not be of equal area isnt it?
대지따라 돌린게 시간이다.. 흘러가고 돌아오지도 않고..
Ivs
Profile Joined January 2008
Australia139 Posts
February 09 2011 10:36 GMT
#7
+ Show Spoiler +

Split the perimeter into 5 equal chunks arbitratily (and none of the chunks are disjoint). Join the 5 boundary points towards the centre of the square with straight lines. The 5 resulting areas satisfy the criteria, since each chunk can be split up into at most 2 triangles, with base on the boundary and a height of 1/2. So each area is 1/2*1/2*4/5=1/5 as required.
endy
Profile Blog Joined May 2009
Switzerland8970 Posts
February 09 2011 10:40 GMT
#8
Which tools can we use ? Is that supposed to be a compass and straightedge construction ?
ॐ
kOre
Profile Blog Joined April 2009
Canada3642 Posts
February 09 2011 10:40 GMT
#9
+ Show Spoiler +
The SQUARE pizza can be treated as a RECTANGULAR pizza with no crust on the left and right side and only crust on the top and bottom. Cut the slices vertically and it should be easy to make them even? Rectangle is fatter and shorter while the square is skinnier and taller making them even? [image loading]
http://www.starcraftmecca.net - Founder
Ivs
Profile Joined January 2008
Australia139 Posts
February 09 2011 10:48 GMT
#10
On February 09 2011 19:36 Ivs wrote:
+ Show Spoiler +

Split the perimeter into 5 equal chunks arbitratily (and none of the chunks are disjoint). Join the 5 boundary points towards the centre of the square with straight lines. The 5 resulting areas satisfy the criteria, since each chunk can be split up into at most 2 triangles, with base on the boundary and a height of 1/2. So each area is 1/2*1/2*4/5=1/5 as required.


+ Show Spoiler +
Oh hey this works for any number of pizza eaters, cool!
SOB_Maj_Brian
Profile Blog Joined September 2008
United States522 Posts
February 09 2011 11:10 GMT
#11
Riser doesn't the middle piece of your solution have 8 units of original crust and all the remaining ones have 7? Or am I missing something here?
evanthebouncy!
Profile Blog Joined June 2006
United States12815 Posts
Last Edited: 2011-02-09 11:17:23
February 09 2011 11:13 GMT
#12
On February 09 2011 19:48 Ivs wrote:
Show nested quote +
On February 09 2011 19:36 Ivs wrote:
+ Show Spoiler +

Split the perimeter into 5 equal chunks arbitratily (and none of the chunks are disjoint). Join the 5 boundary points towards the centre of the square with straight lines. The 5 resulting areas satisfy the criteria, since each chunk can be split up into at most 2 triangles, with base on the boundary and a height of 1/2. So each area is 1/2*1/2*4/5=1/5 as required.


+ Show Spoiler +
Oh hey this works for any number of pizza eaters, cool!


+ Show Spoiler +


Life is run, it is dance, it is fast, passionate and BAM!, you dance and sing and booze while you can for now is the time and time is mine. Smile and laugh when still can for now is the time and soon you die!
evanthebouncy!
Profile Blog Joined June 2006
United States12815 Posts
February 09 2011 11:16 GMT
#13
On February 09 2011 20:10 SOB_Maj_Brian wrote:
Riser doesn't the middle piece of your solution have 8 units of original crust and all the remaining ones have 7? Or am I missing something here?


+ Show Spoiler +

The corner counts twice, so the remaining ones do indeed have 8 perimeters.
Life is run, it is dance, it is fast, passionate and BAM!, you dance and sing and booze while you can for now is the time and time is mine. Smile and laugh when still can for now is the time and soon you die!
HaNdFisH
Profile Blog Joined February 2010
Australia119 Posts
Last Edited: 2011-02-09 11:56:36
February 09 2011 11:29 GMT
#14
Pieces don't have to be the same shape? Just equal amount of outer perimeter taken from edge (inner perimeter okay) and same area?

+ Show Spoiler +

In that case take a triangle out of each side of the pizza (long base edge along crust side) of base 4/5, height 1/2. (this is for square pizza side length 1, can scale to whatever side length). This results in 4 pieces of base (crust) 4/5 units each, leaving 4/5 units of crust for the remaining piece. Each of these pieces has area 1/5 square units, leaving 1/5 for the remaining piece.

*edit* hmm, remaining piece is cut by the others so this doesn't work :<, i guess it depends if you allow the pizza to be counted as one piece when connected by a single point
pksens
Profile Joined July 2010
United Kingdom156 Posts
February 09 2011 11:35 GMT
#15
+ Show Spoiler +
I like drawing 5 pointed stars so I could roughly get 5 points evenly split inside a square. You can then have a cut from the center point through each point or half way point (prefer half way for neatness!)
blue001
Profile Joined January 2009
106 Posts
February 09 2011 11:36 GMT
#16
Ivs - You are smart. Congratuations for the solution
mcht
Profile Joined December 2009
Germany201 Posts
Last Edited: 2011-02-09 11:44:26
February 09 2011 11:44 GMT
#17
+ Show Spoiler +
[image loading]
evanthebouncy!
Profile Blog Joined June 2006
United States12815 Posts
February 10 2011 01:14 GMT
#18
On February 09 2011 20:36 blue001 wrote:
Ivs - You are smart. Congratuations for the solution


yeah he's fcken pro lol it took me 3 days and sleepless dreams hahHAha, i literally jizzed myself when I solved it. Then my friend did it in like 1 minute I was like .____.
Life is run, it is dance, it is fast, passionate and BAM!, you dance and sing and booze while you can for now is the time and time is mine. Smile and laugh when still can for now is the time and soon you die!
JeeJee
Profile Blog Joined July 2003
Canada5652 Posts
Last Edited: 2011-02-10 02:28:11
February 10 2011 02:06 GMT
#19
+ Show Spoiler +

seems pretty simple which means i must be misunderstanding it
but here's what i got (based on the android game sliceit)
so for simplicity's sake let's say its a 5x5 pizza
divide border into 5 cuts, 4 squares long each
from there, make cuts such that each piece is 5 squares in area?
[image loading]

O-o
edit:
come to think of it, you can just cut straight to centre of pizza. should be pretty trivial to see why
(\o/)  If you want it, you find a way. Otherwise you find excuses. No exceptions.
 /_\   aka Shinbi (requesting a name change since 27/05/09 ☺)
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