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  2. Casting out nines - Wikipedia

    en.wikipedia.org/wiki/Casting_out_nines

    If a calculation was correct before casting out, casting out on both sides will preserve correctness. However, it is possible that two previously unequal integers will be identical modulo 9 (on average, a ninth of the time). The operation does not work on fractions, since a given fractional number does not have a unique representation.

  3. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    Note that if n 2 is the closest perfect square to the desired square x and d = x - n 2 is their difference, it is more convenient to express this approximation in the form of mixed fraction as . Thus, in the previous example, the square root of 15 is 4 − 1 8 . {\displaystyle 4{\tfrac {-1}{8}}.}

  4. 9 - Wikipedia

    en.wikipedia.org/wiki/9

    Casting out nines is a quick way of testing the calculations of sums, differences, products, and quotients of integers in decimal, a method known as long ago as the 12th century. [3] If an odd perfect number exists, it will have at least nine distinct prime factors. [4] Non-intersecting chords between four points on a circle

  5. Senary - Wikipedia

    en.wikipedia.org/wiki/Senary

    A number is divisible by 4 if its penultimate digit is odd and its final digit is 2, or its penultimate digit is even and its final digit is 0 or 4. A number is divisible by 5 if the sum of its senary digits is divisible by 5 (the equivalent of casting out nines in decimal). If a number is divisible by 6, then the final digit of that number is 0.

  6. Mental calculator - Wikipedia

    en.wikipedia.org/wiki/Mental_calculator

    A mental calculator or human calculator is a person with a prodigious ability in some area of mental calculation (such as adding, subtracting, multiplying or dividing large numbers). In 2005, a group of researchers led by Michael W. O'Boyle, an American psychologist previously working in Australia and now at Texas Tech University , has used MRI ...

  7. Method of complements - Wikipedia

    en.wikipedia.org/wiki/Method_of_complements

    The smaller numbers, for use when subtracting, are the nines' complement of the larger numbers, which are used when adding. In mathematics and computing , the method of complements is a technique to encode a symmetric range of positive and negative integers in a way that they can use the same algorithm (or mechanism ) for addition throughout ...

  8. Nines (notation) - Wikipedia

    en.wikipedia.org/wiki/Nines_(notation)

    1 troy ounce of four nines fine gold (999.9) Nines are an informal logarithmic notation for proportions very near to one or, equivalently, percentages very near 100%. Put simply, "nines" are the number of consecutive nines in a percentage such as 99% (two nines) [1] or a decimal fraction such as 0.999 (three nines).

  9. Wikipedia : WikiProject Mathematics/List of mathematics ...

    en.wikipedia.org/wiki/Wikipedia:WikiProject...

    Cairo pentagonal tiling-- Cake number-- Calabi conjecture-- Calabi–Eckmann manifold-- Calabi flow-- Calabi triangle-- Calabi–Yau algebra-- Calabi–Yau manifold-- Calculation-- Calculation of glass properties-- Calculator-- Calculator input methods-- Calculatrivia-- Calculus-- Calculus Made Easy-- Calculus of constructions-- Calculus of functors-- Calculus of moving surfaces-- Calculus of ...