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by karakfa
November 25th, 2011, 7:40 pm
Forum: Brainteaser Forum
Topic: making number closest to e
Replies: 18
Views: 73102

making number closest to e

can't be compared with the latest posts but without any tricks (other than bending the rules) we can get 6 decimal pointse ~ for k between 0 and 9.
by karakfa
January 20th, 2011, 8:13 pm
Forum: Brainteaser Forum
Topic: Wine & rats
Replies: 14
Views: 29535

Wine & rats

In this version minimum 10 rats are required but for the sake of the rats you can encode it such that at most 8 will die.
by karakfa
January 7th, 2011, 12:33 am
Forum: Brainteaser Forum
Topic: Card Problem
Replies: 18
Views: 37207

Card Problem

<t>The problem to find E{N} for N(52,13).let's start with a simpler case N(3,1) to enumerate all combinations (which is C(3,1)), interested face is "1" and others ".", we count the remaining cards in the deck.1.. -> 2.1. -> 1..1 -> 0Let S is the sum of all remaining cards, 3 in this caseThe number w...
by karakfa
February 26th, 2010, 8:45 pm
Forum: Brainteaser Forum
Topic: eigenvalue question
Replies: 6
Views: 35828

eigenvalue question

and at that lower bound the min eigenvalue will be zero.ps. by the way that lower bound for alpha is -1/(n-1) where n is the size of the matrix.
by karakfa
February 22nd, 2010, 9:27 pm
Forum: Brainteaser Forum
Topic: Newborns brainteaser
Replies: 18
Views: 39793

Newborns brainteaser

yep, the simplified formula is:p = P(boy born | boy selected) = (b + 1) / (2b + 1), where b is the number of boys initially.some special cases:b=0 -> p=1b->Inf -> p=0.5
by karakfa
September 8th, 2009, 8:39 pm
Forum: Brainteaser Forum
Topic: Maximum Flags
Replies: 6
Views: 36295

Maximum Flags

Here is a solution with your notation:123147158169248259267349357368456789
by karakfa
September 8th, 2009, 8:10 pm
Forum: Brainteaser Forum
Topic: Maximum Flags
Replies: 6
Views: 36295

Maximum Flags

your last two entries are not "obeying" the rule. 359369 The answer is 12.There are C(9,2) = 36 unique pairs of colors. Each flag represents C(3,2) = 3 such pairs, therefore there can be maximum 36/3 = 12 such flags.
by karakfa
June 15th, 2009, 8:58 pm
Forum: Brainteaser Forum
Topic: 3 dice
Replies: 3
Views: 39422

3 dice

More hints:For a 3 sided die (a rounded-off triangular prism will do) use these values:a: 1,6,8b: 2,4,9c: 3,5,7here on average b beats a, c beats b, and a beats c.
by karakfa
June 15th, 2009, 3:57 pm
Forum: Brainteaser Forum
Topic: 3 dice
Replies: 3
Views: 39422

3 dice

<t>This works only for special dice. I guess it was on Scientific American some years ago. You can design the die such thata wins against b, b wins against c, and c wins against a. Note that the expected values will be the same but it's not the same as winning against.Exercise to you is to set up th...
by karakfa
May 13th, 2009, 8:59 pm
Forum: Brainteaser Forum
Topic: Jelly beans
Replies: 20
Views: 44435

Jelly beans

35/16 is correct. everforget: Both can't reach to zero, when one reaches the process ends.
by karakfa
February 26th, 2009, 6:51 pm
Forum: Brainteaser Forum
Topic: What is the optimal strategy for this $ game?
Replies: 12
Views: 45224

What is the optimal strategy for this $ game?

typo fixed above
by karakfa
December 5th, 2006, 5:35 pm
Forum: Brainteaser Forum
Topic: Sum of dices problem
Replies: 8
Views: 88613

Sum of dices problem

well, that doesn't give you the probability.check this old post for a related Q.
by karakfa
October 19th, 2006, 6:02 pm
Forum: Brainteaser Forum
Topic: Interview Brainteaser
Replies: 5
Views: 91765

Interview Brainteaser

also don't forget the option value of continuing with the game until you hit the million.
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