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  2. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    For any 2-digit by 2-digit multiplication problem, if both numbers end in five, the following algorithm can be used to quickly multiply them together: [1] E x : 35 × 75 {\displaystyle \mathrm {Ex} :35\times 75}

  3. Multiplication table - Wikipedia

    en.wikipedia.org/wiki/Multiplication_table

    In 493 AD, Victorius of Aquitaine wrote a 98-column multiplication table which gave (in Roman numerals) the product of every number from 2 to 50 times and the rows were "a list of numbers starting with one thousand, descending by hundreds to one hundred, then descending by tens to ten, then by ones to one, and then the fractions down to 1/144."

  4. 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; 41 / 2 ⁠ × 21 / 2 ⁠ = 11 ⁠ 1 / 4

  5. Collatz conjecture - Wikipedia

    en.wikipedia.org/wiki/Collatz_conjecture

    For instance, the first counterexample must be odd because f(2n) = n, smaller than 2n; and it must be 3 mod 4 because f 2 (4n + 1) = 3n + 1, smaller than 4n + 1. For each starting value a which is not a counterexample to the Collatz conjecture, there is a k for which such an inequality holds, so checking the Collatz conjecture for one starting ...

  6. Elementary arithmetic - Wikipedia

    en.wikipedia.org/wiki/Elementary_arithmetic

    When two numbers are multiplied, the resulting value is a product. The numbers being multiplied are multiplicands, multipliers, or factors. Multiplication can be expressed as "five times three equals fifteen," "five times three is fifteen," or "fifteen is the product of five and three."

  7. 1 + 2 + 3 + 4 + ⋯ - ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E...

    where f (2k−1) is the (2k − 1)th derivative of f and B 2k is the (2k)th Bernoulli number: B 2 = ⁠ 1 / 6 ⁠, B 4 = ⁠− + 1 / 30 ⁠, and so on. Setting f ( x ) = x , the first derivative of f is 1, and every other term vanishes, so [ 15 ]

  8. Multiplication and repeated addition - Wikipedia

    en.wikipedia.org/wiki/Multiplication_and...

    Multiplication can also be thought of as scaling. In the above animation, we see 3 being multiplied by 2, giving 6 as a result. One theory of learning multiplication derives from the work of the Russian mathematics educators in the Vygotsky Circle which was active in the Soviet Union between the world wars. Their contribution is known as the ...

  9. Product (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Product_(mathematics)

    In mathematics, a product is the result of multiplication, or an expression that identifies objects (numbers or variables) to be multiplied, called factors.For example, 21 is the product of 3 and 7 (the result of multiplication), and (+) is the product of and (+) (indicating that the two factors should be multiplied together).