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Everything posted by bonanova

  1. Heads up

    Alternate approach to the ant-checkerboard problem asks: What is the probability of flipping 8 heads before 5 tails?
  2. Heads up

  3. Tempus fugit

    I was born at 11:35pm Central time in the United States on yesterday's date. The fact that I now live in the Eastern time zone might have moved my birthday to today's date. IDK. I don't know how these things work, nor in the grand scheme whether it even matters. I suspect it doesn't. The point of writing this, is the shock I had last night when friends took me out to dinner, good chicken and ribs btw, and one of them said to me, so you're __ years old now. My reaction was to say "no way" until I realized they had it right. And I thought once again about my mortality. My grandfather lived to within days of his 100th birthday, and I've always had it in the back of my mind that I would finish that journey in his honor -- even tho it might entail outliving certain government benefits. But one never knows. BrainDen community lost SuperPrismatic this year, at an age much less than mine at present. But not to be morbid. Que sera, sera, and let's celebrate the day, each day. I heard from all my children and grandchildren yesterday, and life is good.
  4. derivative brain teaser

    Looks like ...
  5. Next card is Red

    @CaptainEd shuffles a standard deck of playing cards and begins dealing the cards face up on the table. At any time @plainglazed can say Stop and bet $1 that the next card will be red. If he does not interrupt, the bet will automatically be placed on the last card. What is the best strategy? How much better than 50% can @plainglazed do?
  6. Heads up

    That was the first-cut answer in the ant-chessboard problem. The solution is easier to find if we (reasonably) assume that
  7. Balancing weights

  8. Breaking a three-way tie

    Al, Bert and Charlie are on the ballot for secretary of the local yacht club, and they finish in a three-way tie. To break it, they solicit the members' second choices, and again it's a three-way tie. Al notes that since the number of members is odd, a series of two-way votes would be decisive. As a reward for finding a way past the impasse, Al receives the bye and will take on the winner of a Bert vs Charlie vote to decide who gets the position as secretary. Assuming voter preferences do not change, what are the winning probabilities for the three gentlemen?
  9. I'm humbled. btw I sharpened (with humor) the flavor text and posted this on another favorite site. It will be interesting to see how quickly it's solved there.
  10. @Molly Mae gets the coveted bonanova gold star for finding an algorithm and getting the answer in less than one day. So now that the cat (algorithm) is out of the bag, so to speak, it should be trivial to find whether an integer can triple, (or quadruple, or quintuple) under the same manipulation. It's also interesting that his solution forms a ring that shows the doubling process also occurs for four other ending digits (not 1, so his is the smallest.) But which ones? Incidentally, this also shows that all such integers have 18 digits.
  11. a barrel of pickles

    Fun one.
  12. Baggage on a conveyor belt

    The answer probably does change with the nature of the distances.
  13. Ants on a checkerboard

    Two ants named Al and Bert sit at diagonal corners of a checkerboard and decide to change places. Al, at the lower left, walks randomly upward or to the right, and Bert, at the upper right, walks randomly downward or to the left. They follow the boundaries of the checkerboard squares. That is, except when following the extreme boundary of the checkerboard, their left and right feet always touch squares of opposite color. What is the probability of their meeting (1) if they walk at the same speed, or (2) if Al walks 3 times as fast as Bert?
  14. Ants on a checkerboard

    Regarding the 5 probabilities after 12 ant moves:
  15. making obtuse triangles

    Case by case results, inviting algorithm falsification, while limiting lengths to 10.
  16. Sorting out the bar bill

    A bunch of friends went to the sports bar and got a group rate on the drinks: $5/glass for wine, $2/glass for beer, and $1/glass for water. When we left, the waiter asked me to sort out the bill. There was enough uncertainty in what people remembered that I could not be precise. So we happily just threw in enough to cover the bill, which came to $293 and we went home. But it got me thinking. None of us had multiple glasses of the same beverage. The waiter said 106 glasses were used, once each. 18 of us did not drink water. 39 people had wine. I was certain that 9 of us were teetotalers. If I had known the sizes of just three classes of drinkers I could have figured out the bill, as it was, I could not. But it did occur to me that if those who drank beer and water but not wine were as many as possible, and if those who drank only wine were half as many as that, I could say the smallest number of us who drank all three. Can you?
  17. making obtuse triangles

    I get fewer ...
  18. Coin hunt

    Naively.I might want the first n-1 coins to be heads if the valuable one was tails in the nth position. I'd have you keep flipping them until they showed heads. But /// I watched the video, so ... nah.
  19. Coin hunt

    I can ask you to flip a coin for a 2nd time?
  20. Sorting out the bar bill

    @Pickett It may not impact your solution, but the OP did not intend to say that all of us drank something. "Class of drinkers" was not meant to preclude anyone from drinking nothing. Meaning there are eight "classes" of drinkers. Sorry for that. I have this thing about insisting that zero is a number, rather than a denial. Also, I get a different answer. I'll check my analysis against yours to see why.
  21. Sorting out the bar bill

    It means that all of the teetotalers drank neither wine nor beer. Let's say also that the others did consume alcohol. One class of friends may have drunk nothing, and perforce not used a glass.
  22. Coin hunt

    Thinking. Meantime I'll call your 10 minutes of cat flight and raise you 25 minutes of Roomfull of Teeth, as they explore new uses for the human voice, which you might actually enjoy.
  23. Next card is Red

    Let there be n red cards and n black cards.
  24. When midnight strikes

    At an ever increasing pace Al, Bert and Charlie have been receiving into three identical boxes of limitless capacity identical pairs of silver coins engraved with the integers 1, 2, 3, 4, ... etc. These events occur on a precise schedule, each box receiving Coins marked 1 and 2 at 1 minute before midnight Coins marked 3 and 4 at 1/2 minute before midnight Coins marked 5 and 6 at 1/4 minute before midnight Coins marked 7 and 8 at 1/8 minute before midnight etc. But they were instructed at each event to remove a coin from their respective boxes and discard it. After some thought, Al decided each time to discard his lowest-numbered coin; Bert discarded an even-numbered coin; and Charlie thought what the heck and discarded a coin selected at random. Regardless of strategy, at each event the number of coins in each box grew by unity, so that after N events each box held N coins. Needless to say when midnight struck their arms were infinitely tired, but it was a small price to pay for infinite riches. But tell us, now, whether their expectations were met. Describe the contents of each box at midnight.