1000 Point Star
Logic puzzles require you to think. You will have to be logical in your reasoning.
Typical "stars" are drawn in connected, but not repeated, line segments. For example, a 5point star is drawn as such  line segments AC, CE, EB, BD, DA. The segments must always alternate a constant number of points (in the above case, skipping 1 point in between).
Given the information that there is only 1 way to draw a 5point star, and that there is NO way to draw a 6point star (in continuous lines, that is), and there are 2 ways to draw a 7point star, how many different ways are there to draw a 1000point star?
HintIt's not guess work. Think of factors and mirror images. Try drawing out examples.
Hide
Answer
199.
First, let's examine the 5point star and why there is only that one, described, way to draw it. Starting at A, you cannot go straight to point B, otherwise you will have a pentagon, not a star. Same with point E. AC and AD (and their progressions) yield identical pictures (notice that the last segment in the AC one is DA, literally reverse all the letters to get AD ending in CA).
Now, for a 6point star, there are points A, B, C, D, E, and F. Starting at A, we cannot go to B or F, because then we have a hexagon. If we go AC, then we must go CE, then CA... making a triangle, not a 6point star. Going backwards, AE, EC, EA; mirror image. If we skip 2 points, we go AD, then DA, a straight line, hardly a 6point star.
For a 7point star, AG, AB and AG are not possible, as that's a heptagon. AC, CE, EG, GB, BD, DF, FA is one way to draw the star, skipping one point in between. Also, AD, DG, GC, CF, FB, BE, EA, skipping two points in between each, is the other way. The last two line possibilities, AF and AE are mirror images of the two working scenarios.
Examining the above information a little more deeply, we see that we must divide all possible drawings by two, to get rid of the mirror images. Also, we cannot use the point immediately to the left, that is AB as a segment. This explains why there is only 1 way for a 5point, and 2 for a 7point, but does not explain the 6point. Of those remaining points (dealing only with the first half, again, mirror images), those that are factors of the number of total points do not work, because you will end up back at the starting point before hitting every number. AC is a factor in six because it passes point B, so it's 2. AD is a factor of 3 (B, C and D). Not only factors, but multiples of factors, as well (for example, skipping 4 points in the 6point still does not work).
Using the knowledge of mirrors, first point impossibility (AB) and factors, we see that the number 1000 is made up of 10^3, or 2^3*5^3. Without going through every factor, it's quickly and easily discernible that of the numbers 11000, 2 or multiples of it encompass 500 numbers, all evens. Any multiple of 5 includes 200 numbers, half of which end in 0 and are already included with the 2's, so there are 600 unique factors and multiples between 1 and 1000. That leaves us with 400 that are *not*, which should explain how many unique stars we can make. Remember to cut it in half because of mirroring, leaving us with 200, and to discount the AB segment (factor of 1), leaving us with 199. (If you discount AB, and THEN halve it, remember you needed to remove A[Z], the mirror image of that point).
Hide
Comments
HiImDavid
Sep 04, 2006
 Wow, very nice. It looks liek you invested a lot of time into that one!!! Very nice 
Punk_Rocker
Sep 05, 2006
 Someone has wayyy too much free time. xD
Interesting, though...That was cool. 
soccerfreak
Sep 05, 2006
 how ling did it take u to do this?

jazzmusician46
Sep 06, 2006
 My goodness! 
Infrared
Sep 18, 2006
 Waaaaay too complicated or me.
Great job. Must've been very timeconsuming. 
googoogjoob
Sep 20, 2006
 Got me on this one! I've been interested in multipointed stars ever since a 9pointed star showed up in a math contest I once entered in middle school. So this one was a lot of fun for me, even though I came up with a wrong answer. 
ulan
Oct 19, 2006
 Good puzzle, not so diffucult of one know about phi 
Matio_Mario
Oct 29, 2006
 Ugh! Math is my best subject, but at the end I'm like "WHAT?!?!?!? Is this English???" 
NomadShadow
Nov 08, 2006
 In the course of my job I usually have to do alot of modulus arithmetics, so this took me less than 10 seconds to figure out.
Cool one though, this is the first time I think of stars as ranges.
Keep up the good work 
qwertyopiusa
Nov 29, 2006
 Nice problem! 
stil
Dec 02, 2006
 Confusing use of "star" and "repeated line segment."
Hope to effect correction. 
McBobby1212
Mar 02, 2007
 ...what?... 
sftball_rocks13
Mar 25, 2007
 wow...that was hard
the answer was long. very long. it scared me
good teaser
scary teaser 
Odessius
Apr 26, 2007
 i dunno, a million? yet i think that defeats the purpose of brain logic. still just grab a pencil and that ones pretty easy. for some people 
sarggames
Oct 27, 2014
 please help me out.my answer is 407 or 408.
my working
all points lie on a circle .
there will be n points and gaps between points.
let us fix a point from where we start .
now for moment we move clockwise .
the number of gaps between starting point and first joined point must not be factor of n .if we move around joining points with strategy given the nearest point in the direction opposite to witch we start will have let us say r number of gaps with starting point(in one rotation).let us say number of gaps we are skipping is p.then r is remainder if we divide n by p.
from easy visualization we can observe that must not be a factor of p
if r is a factor of p then r is factor of n buy euclid rules .n=p(some value let us say q)+r .
we want to exclude all p such that r is factor of it .so we must exclude all divisors of nr where r is factor of n.since in the above case we have to skip no of gaps less than 500 to avoid mirror images .so p have a limit .now using counting of all the number to be excluded .i got my answer which is no close to the given one .there might be a counting mistake but not so much please help 
Back to Top
 

Follow Braingle!