SERVING THE QUANTITATIVE FINANCE COMMUNITY

kr
Posts: 1885
Joined: September 27th, 2002, 1:19 pm

### Brainteaser

no, for basically the same reason as the following similar but somewhat more original problem: 1) Start with a 2n x 2n grid2) Number the cells 1 to 4n^2, i.e. 1 to 2n in the first row, 2n+1 to 4n in the second row, etc.3) Color half of the squares black and all the remaining squares red, so that in each row and in each column, half of the squares are black.4) Show that sum of black squares = sum of red squares(from Putnam 2001)

WaaghBakri
Posts: 732
Joined: March 21st, 2002, 4:07 am

### Brainteaser

That was quick. Nice. Had'nt heard of the generalization, but see that it is...Now here's a real toughie for the associationally constrained ....Divide the area bounded by a circle in ten parts using ONLY three lines.

kr
Posts: 1885
Joined: September 27th, 2002, 1:19 pm

### Brainteaser

see, I started to have this shadow of an idea:- you pump out a lot of decent brainteasers- people who read Wilmott tell their friends and pretty soon the 'people in the know' are aware of these new brainteasers- then, when you go to your next interview, if you posed a really good brainteaser, it will come right back to you! And, since you're the guy who spread the virus, you are specially equipped with the antidote, hopefully allowing you to capitalize on the idea.Johnny, if you are reading this, you will recognize your own teachings here... many thanks.

WaaghBakri
Posts: 732
Joined: March 21st, 2002, 4:07 am

### Brainteaser

Not guilty as charged. No consipiracies here. Just happened to come across a few of these yesterday..... so thought I'd toss them out. I've always enjoyed reading these when posed by others, and am only sharing the one's I've come across. Felt some might enjoy them without having to hunt them down. Besides, with reference to interviews, surely the seemingly almighty interviewer can cook up a few originals. Can they not? But then, perhaps not, not everyone is an Aaron. If "interviewers" get perturbed over the fact that interesting brainteaser/interview questions are being posted on a thread, then I think they better re-question their own abilities and get off their high horse & come down to earth .....

WaaghBakri
Posts: 732
Joined: March 21st, 2002, 4:07 am

### Brainteaser

kr, I'm not sure the reason for your accusations. I am beginning to suspect whether it was my use of the words "associationally constrained" and the fact that it followed your post? If so, please rest assured that there are no negative connotations implied in my use of the word "constrained." The choice of words are in fact a hint that don't take the problem seriously. The terminology is borrowed from problem-solving, as in "association constraint." Specifically, don't associate lines with linear segments or straight lines. Given the trivial nature of the solution, I just didn't want people spending too much time on it. Hence, my hint ....

kr
Posts: 1885
Joined: September 27th, 2002, 1:19 pm

### Brainteaser

sorry sorry - I think the tone of my note wasn't that clear...to clarify: I think circulating new brainteasers that are good is an excellent idea - seriouslyif you are the master of brainteasers, then you will be able to answer most of them and hence your interviewing results will be top-notch!so keep up the good work - I don't mind front-running these things either!

mj
Posts: 3449
Joined: December 20th, 2001, 12:32 pm

### Brainteaser

QuoteOriginally posted by: WaaghBakriThat was quick. Nice. Had'nt heard of the generalization, but see that it is...Now here's a real toughie for the associationally constrained ....Divide the area bounded by a circle in ten parts using ONLY three lines.if the lines have to be straight it looks imposs.If they dont, you can do it with two...MJ

Sasquatch
Posts: 36
Joined: March 3rd, 2003, 8:11 pm

### Brainteaser

QuoteOriginally posted by: WaaghBakriThat was quick. Nice. Had'nt heard of the generalization, but see that it is...Now here's a real toughie for the associationally constrained ....Divide the area bounded by a circle in ten parts using ONLY three lines.Is the circle on a piece of paper . . . in other words, in a compact space? Then I can consider the outside of the circle to be area bounded by the circle too, and divide the outside into nine sections with three tangent lines. I can't see how to get ten . . . unless you also consider the inside of the circle (also bounded) to be divided by the circle itself (which I would say isn't very clean).

Chukchi
Posts: 915
Joined: December 15th, 2001, 3:43 am

### Brainteaser

Last edited by Chukchi on November 13th, 2003, 11:00 pm, edited 1 time in total.

sdw
Posts: 61
Joined: January 16th, 2003, 12:29 pm

### Brainteaser

This one's good:There is an isolated community where each person has either a white spot or a black spot on their forehead. Nobody knows what the colour of their own spot is, but if they find out, they immediately commit suicide.An outsider comes into the community and announces to everybody that at least one person has a white spot.What happens?

Nonius
Posts: 5115
Joined: January 22nd, 2003, 6:48 am

### Brainteaser

QuoteOriginally posted by: sdwThis one's good:There is an isolated community where each person has either a white spot or a black spot on their forehead. Nobody knows what the colour of their own spot is, but if they find out, they immediately commit suicide.An outsider comes into the community and announces to everybody that at least one person has a white spot.What happens?everyone dies! muhuhahahaa.......

FDAXHunter
Posts: 3824
Joined: November 5th, 2002, 4:08 pm

### Brainteaser

Everyone dies and I feed on their corpses, then I kill the outsider and have the whole island to myself.

sdw
Posts: 61
Joined: January 16th, 2003, 12:29 pm

### Brainteaser

QuoteOriginally posted by: FDAXHunterEveryone dies and I feed on their corpses, then I kill the outsider and have the whole island to myself.Just like on a normal Saturday night then? . . .

FDAXHunter
Posts: 3824
Joined: November 5th, 2002, 4:08 pm

### Brainteaser

sdw: Just like on a normal Saturday night then? . .Why don't you come to my island Saturday and find out?..... Muhahahhahaha

sdw
Posts: 61
Joined: January 16th, 2003, 12:29 pm

### Brainteaser

QuoteOriginally posted by: FDAXHunter<b>sdw: </b><i>Just like on a normal Saturday night then? . .</i>Why don't you come to my island Saturday and find out?..... MuhahahhahahaEh . . .. I'm busy. I have ..... to . . . . get my bike fixed that night. Bye!

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