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Everything posted by bonanova

  1. bonanova

    New math

    If 5+3+2 = 151022 9+2+4 = 183652 8+6+3 = 482466 5+4+5 = 202541 Then 7+5+2 = ______ ?
  2. Can you write down a 9-letter word that permits you to erase it, one letter at a time, such that after each erasure a valid (English) word remains? (As implied, the letter order remains the same throughout.) Clue: Example:
  3. bonanova

    Same numbers of heads

    @Thalia You are so right. Thanks. Locking this thread.
  4. bonanova

    Same numbers of heads

    Twenty coins lie on a table, with ten coins showing heads and the other ten showing tails. You are seated at the table, blindfolded and wearing gloves. You are tasked with creating two groups of coins, with each group showing the same numbers of heads (and tails) as the other group. You are only permitted to move or flip coins, and you are unable to determine their initial state. What's your plan?
  5. bonanova

    Dividend please (on steroids)

    It's an alternative representation to put the quotient to the right side. Here is the more familiar placement. The green (overlined) digits repeat forever. _________________ x x x x x x x x x x x x -------------- x x x x x x / x x x x x x x x x x x x x ----------- x x x x x x x x x x x x x ----------- x x x x x x x x x x x x x x ------------- x x x x x x x x x x x x x ------------- x x x x x x x x x x x x x x ------------- x x x x x x x x x x x x x x ------------- x x x x x x x x x x x x x x ------------- x x x x x x x x x x x x x x ------------- x x x x x x x x x x x x ----------- x x x x x x
  6. bonanova

    Dividend, please?

    Here are the placeholders for a long division, along with a single digit in the quotient. Can you piece together the dividend? x 7 x x x ---------------- x x x / x x x x x x x x x x x x ------- x x x x x x ----- x x x x x x x ----------- x x x x x x x x ------- - - - - -------
  7. bonanova

    Dividend, please?

  8. Things are not going well at the Acme Company. Executive talent is hard to come by, and it is not cheap. Folks at the water cooler have no ideas, and the coffee-breakers can't imagine how to improve things either. But those who party around the teapot, they came up with something. They suggested to the Board that Acme promote the newest hire in the mail room and make him the CEO! We need to shake things up, but good. Qualifications, job experience, brains, judgment, integrity, these are all things of the past. Some were not so sure. Doesn't make sense at all, the old timers said. Almost like appointing some guy with orange complexion to be President. That's exactly the idea, said the tea-people. Turn things on end, let the bull loose in the china shop, and see what happens. Hey -- how could it be worse than what we have now? Not surprisingly, the debate was long and heated. Such a risk merited proof of possible gain, so the old guard posed a challenge: produce a concrete example of where the idea had been tried with incontrovertible benefit. In fact, make it mathematical. You know, something that might make a good BrainDen puzzle. We'll promote the mail room guy, they said, if you can show us an integer that doubles in value when its least significant digit is promoted to its most-significant position. That is, give us a number { some digits } q that has half the value of q { same digits }. That all happened last week, and now we're looking for the mail room guy. Was he promoted? Did the tea people find such a number? Is there one? We need a number or a proof that one does not exist. T.L.D.R. What number doubles in value by by moving its last digit to the first position (if there is one)?
  9. bonanova

    Heads up

  10. bonanova

    Heads up

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

    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.
  12. bonanova

    derivative brain teaser

    Looks like ...
  13. bonanova

    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?
  14. bonanova

    Heads up

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

    Balancing weights

  16. bonanova

    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?
  17. 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.
  18. @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.
  19. bonanova

    a barrel of pickles

    Fun one.
  20. bonanova

    Baggage on a conveyor belt

    The answer probably does change with the nature of the distances.
  21. bonanova

    Ants on a checkerboard

    Regarding the 5 probabilities after 12 ant moves:
  22. bonanova

    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?
  23. bonanova

    making obtuse triangles

    Case by case results, inviting algorithm falsification, while limiting lengths to 10.