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  2. Sums of three cubes - Wikipedia

    en.wikipedia.org/wiki/Sums_of_three_cubes

    The case = of this problem was used by Bjorn Poonen as the opening example in a survey on undecidable problems in number theory, of which Hilbert's tenth problem is the most famous example. [57] Although this particular case has since been resolved, it is unknown whether representing numbers as sums of cubes is decidable.

  3. Missing dollar riddle - Wikipedia

    en.wikipedia.org/wiki/Missing_dollar_riddle

    There seems to be a discrepancy, as there cannot be two answers ($29 and $30) to the math problem. On the one hand it is true that the $25 in the register, the $3 returned to the guests, and the $2 kept by the bellhop add up to $30, but on the other hand, the $27 paid by the guests and the $2 kept by the bellhop add up to only $29.

  4. Casting out nines - Wikipedia

    en.wikipedia.org/wiki/Casting_out_nines

    The digit sum of 2946, for example is 2 + 9 + 4 + 6 = 21. Since 21 = 2946 − 325 × 9, the effect of taking the digit sum of 2946 is to "cast out" 325 lots of 9 from it. If the digit 9 is ignored when summing the digits, the effect is to "cast out" one more 9 to give the result 12.

  5. The monkey and the coconuts - Wikipedia

    en.wikipedia.org/wiki/The_monkey_and_the_coconuts

    The problem is so well known that the entire class is often referred to broadly as "monkey and coconut type problems", though most are not closely related to the problem. Another example: "I have a whole number of pounds of cement, I know not how many, but after addition of a ninth and an eleventh, it was partitioned into 3 sacks, each with a ...

  6. Ages of Three Children puzzle - Wikipedia

    en.wikipedia.org/wiki/Ages_of_Three_Children_puzzle

    The Ages of Three Children puzzle (sometimes referred to as the Census-Taker Problem [1]) is a logical puzzle in number theory which on first inspection seems to have insufficient information to solve. However, with closer examination and persistence by the solver, the question reveals its hidden mathematical clues, especially when the solver ...

  7. List of undecidable problems - Wikipedia

    en.wikipedia.org/wiki/List_of_undecidable_problems

    In the ray tracing problem for a 3-dimensional system of reflective or refractive objects, determining if a ray beginning at a given position and direction eventually reaches a certain point. [ 15 ] Determining if a particle path of an ideal fluid on a three dimensional domain eventually reaches a certain region in space.

  8. Talk:Missing dollar riddle - Wikipedia

    en.wikipedia.org/wiki/Talk:Missing_dollar_riddle

    Now that each of the guests has been given $1 back, each has paid $9, and each has an extra, unexpected profit of $1 bringing the total paid to $27 and the total refund to $3. The bellhop has 2 dollars which is subtracted from the total amount paid to the hotel of $27, as this was stolen by the bellhop from the $27 the guests had "paid" to the ...

  9. List of unsolved problems in mathematics - Wikipedia

    en.wikipedia.org/wiki/List_of_unsolved_problems...

    Many mathematical problems have been stated but not yet solved. These problems come from many areas of mathematics, such as theoretical physics, computer science, algebra, analysis, combinatorics, algebraic, differential, discrete and Euclidean geometries, graph theory, group theory, model theory, number theory, set theory, Ramsey theory, dynamical systems, and partial differential equations.