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  2. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    The products of small numbers may be calculated by using the squares of integers; for example, to calculate 13 × 17, one can remark 15 is the mean of the two factors, and think of it as (15 − 2) × (15 + 2), i.e. 15 22 2.

  3. Trachtenberg system - Wikipedia

    en.wikipedia.org/wiki/Trachtenberg_system

    Take half of the neighbor, then, if the current digit is odd, add 5. Example: 42×5=210 Half of 2's neighbor, the trailing zero, is 0. Half of 4's neighbor is 1. Half of the leading zero's neighbor is 2. 43×5 = 215 Half of 3's neighbor is 0, plus 5 because 3 is odd, is 5. Half of 4's neighbor is 1. Half of the leading zero's neighbor is 2. 93 ...

  4. 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 ...

  5. Mental abacus - Wikipedia

    en.wikipedia.org/wiki/Mental_abacus

    Mental calculation is said to improve mental capability, increases speed of response, memory power, and concentration power. Many veteran and prolific abacus users in China, Japan, South Korea, and others who use the abacus daily, naturally tend to not use the abacus any more, but perform calculations by visualizing the abacus.

  6. Alberto Coto García - Wikipedia

    en.wikipedia.org/wiki/Alberto_Coto_García

    Alberto Coto García (born May 20, 1970) is a Spanish mental calculator. He was the world champion in mental calculation from 2008 to 2010. Professionally he is a financial adviser and accountant. He has demonstrated his skills and has appeared on some TV shows and news [citation needed]. In recent years he has carried out demonstrations and ...

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