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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

    The Trachtenberg system is a system of rapid mental calculation.The system consists of a number of readily memorized operations that allow one to perform arithmetic computations very quickly.

  4. Arithmetic - Wikipedia

    en.wikipedia.org/wiki/Arithmetic

    For instance, if the number π is rounded to 4 decimal places, the result is 3.142 because the following digit is a 5, so 3.142 is closer to π than 3.141. [107] These methods allow computers to efficiently perform approximate calculations on real numbers.

  5. Portal:Arithmetic - Wikipedia

    en.wikipedia.org/wiki/Portal:Arithmetic

    Therefore, the difference of 5 and 2 is 3; that is, 5 − 2 = 3. While primarily associated with natural numbers in arithmetic , subtraction can also represent removing or decreasing physical and abstract quantities using different kinds of objects including negative numbers , fractions , irrational numbers , vectors , decimals, functions, and ...

  6. Order of operations - Wikipedia

    en.wikipedia.org/wiki/Order_of_operations

    [2] [3] Thus, in the expression 1 + 2 × 3, the multiplication is performed before addition, and the expression has the value 1 + (2 × 3) = 7, and not (1 + 2) × 3 = 9. When exponents were introduced in the 16th and 17th centuries, they were given precedence over both addition and multiplication and placed as a superscript to the right of ...

  7. Multiplication table - Wikipedia

    en.wikipedia.org/wiki/Multiplication_table

    In mathematics, a multiplication table (sometimes, less formally, a times table) is a mathematical table used to define a multiplication operation for an algebraic system. The decimal multiplication table was traditionally taught as an essential part of elementary arithmetic around the world, as it lays the foundation for arithmetic operations ...

  8. Multiplication - Wikipedia

    en.wikipedia.org/wiki/Multiplication

    Here, 2 is being multiplied by 3 using scaling, giving 6 as a result. Animation for the multiplication 2 × 3 = 6 4 × 5 = 20. The large rectangle is made up of 20 squares, each 1 unit by 1 unit. Area of a cloth 4.5m × 2.5m = 11.25m 2; 4 ⁠ 1 / 2 ⁠ × 2 ⁠ 1 / 2 ⁠ = 11 ⁠ 1 / 4 ⁠

  9. Calculator input methods - Wikipedia

    en.wikipedia.org/wiki/Calculator_input_methods

    On a single-step or immediate-execution calculator, the user presses a key for each operation, calculating all the intermediate results, before the final value is shown. [1] [2] [3] On an expression or formula calculator, one types in an expression and then presses a key, such as "=" or "Enter", to evaluate the expression.