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Rack-O (Posted on 2006-10-10) Difficulty: 3 of 5
Take a deck of cards labeled 1-60. Shuffle well and flip over the first 10 cards in a row from left to right.

Let x represent the number of cards in a row from the left that are in ascending order.

For example if the cards were 3 15 22 59 40 7 19 30 33 34 then x=4. The streak ends with the 59 because 40 is less.

Find a formula for p(x), the probability the first x cards are in ascending order and card x+1 is lower than card x, where x={1,...,10}

Generalize: For a deck of c cards labeled 1 to c and flipping over a row of n cards. Find a formula for p(x) where x={1,...,n}

  Submitted by Jer    
Rating: 4.6667 (3 votes)
Solution: (Hide)
c is a red-herring. The cards may as well be numbered 1 through n. Suprisingly, n doesn't matter much either.

If x is less than n then p(x)=(x-1)/x!
If x = n then p(x)=1/x!

The derivation by Joel is the 4th comment and should suffice.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
re: Wow!Joel2006-10-11 17:29:05
Wow!Steve Herman2006-10-11 08:15:03
Hints/Tipsre: Solution ........ please reconsiderAdy TZIDON2006-10-10 15:54:32
SolutionSolutionJoel2006-10-10 12:46:53
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