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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 2 − 2 2.

  3. Modular arithmetic - Wikipedia

    en.wikipedia.org/wiki/Modular_arithmetic

    Primitive root modulo m: A number g is a primitive root modulo m if, for every integer a coprime to m, there is an integer k such that g k ≡ a (mod m). A primitive root modulo m exists if and only if m is equal to 2, 4, p k or 2p k, where p is an odd prime number and k is a positive integer.

  4. Calculator - Wikipedia

    en.wikipedia.org/wiki/Calculator

    The Arithmometer, invented in 1820 as a four-operation mechanical calculator, was released to production in 1851 as an adding machine and became the first commercially successful unit; forty years later, by 1890, about 2,500 arithmometers had been sold [16] plus a few hundreds more from two arithmometer clone makers (Burkhardt, Germany, 1878 ...

  5. Windows Calculator - Wikipedia

    en.wikipedia.org/wiki/Windows_Calculator

    A simple arithmetic calculator was first included with Windows 1.0. [5]In Windows 3.0, a scientific mode was added, which included exponents and roots, logarithms, factorial-based functions, trigonometry (supports radian, degree and gradians angles), base conversions (2, 8, 10, 16), logic operations, statistical functions such as single variable statistics and linear regression.

  6. Mathematics - Wikipedia

    en.wikipedia.org/wiki/Mathematics

    Mathematics is a field of study that discovers and organizes methods, theories and theorems that are developed and proved for the needs of empirical sciences and mathematics itself.

  7. Divisibility rule - Wikipedia

    en.wikipedia.org/wiki/Divisibility_rule

    Calculate the remainders left by each product on dividing by 7. Add these remainders. The remainder of the sum when divided by 7 is the remainder of the given number when divided by 7. For example: The number 194,536 leaves a remainder of 6 on dividing by 7. The number 510,517,813 leaves a remainder of 1 on dividing by 7.

  8. Battery charger - Wikipedia

    en.wikipedia.org/wiki/Battery_charger

    A battery charger, recharger, or simply charger, [1] [2] is a device that stores energy in an electric battery by running current through it. The charging protocol—how much voltage and current, for how long and what to do when charging is complete—depends on the size and type of the battery being charged.

  9. Rule of 72 - Wikipedia

    en.wikipedia.org/wiki/Rule_of_72

    To estimate the number of periods required to double an original investment, divide the most convenient "rule-quantity" by the expected growth rate, expressed as a percentage. For instance, if you were to invest $100 with compounding interest at a rate of 9% per annum, the rule of 72 gives 72/9 = 8 years required for the investment to be worth ...