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  2. Trachtenberg system - Wikipedia

    en.wikipedia.org/wiki/Trachtenberg_system

    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. It was developed by the Ukrainian engineer Jakow Trachtenberg in order to keep his mind occupied while being in a Nazi concentration ...

  3. Chisanbop - Wikipedia

    en.wikipedia.org/wiki/Chisanbop

    Chisanbop or chisenbop (from Korean chi (ji) finger + sanpŏp (sanbeop) calculation [1] 지산법/指算法), sometimes called Fingermath, [2] is a finger counting method used to perform basic mathematical operations. According to The Complete Book of Chisanbop[3] by Hang Young Pai, chisanbop was created in the 1940s in Korea by Sung Jin Pai ...

  4. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    Since 9 = 10 − 1, to multiply a number by nine, multiply it by 10 and then subtract the original number from the result. For example, 9 × 27 = 270 − 27 = 243. This method can be adjusted to multiply by eight instead of nine, by doubling the number being subtracted; 8 × 27 = 270 − (2×27) = 270 − 54 = 216.

  5. Divisibility rule - Wikipedia

    en.wikipedia.org/wiki/Divisibility_rule

    [9] Another method is multiplication by 3. A number of the form 10x + y has the same remainder when divided by 7 as 3x + y. One must multiply the leftmost digit of the original number by 3, add the next digit, take the remainder when divided by 7, and continue from the beginning: multiply by 3, add the next digit, etc.

  6. Multiplication algorithm - Wikipedia

    en.wikipedia.org/wiki/Multiplication_algorithm

    Multiplication algorithm. A multiplication algorithm is an algorithm (or method) to multiply two numbers. Depending on the size of the numbers, different algorithms are more efficient than others. Numerous algorithms are known and there has been much research into the topic. The oldest and simplest method, known since antiquity as long ...

  7. Casting out nines - Wikipedia

    en.wikipedia.org/wiki/Casting_out_nines

    Casting out nines is any of three arithmetical procedures: [1] Adding the decimal digits of a positive whole number, while optionally ignoring any 9s or digits which sum to 9 or a multiple of 9. The result of this procedure is a number which is smaller than the original whenever the original has more than one digit, leaves the same remainder as ...

  8. FOIL method - Wikipedia

    en.wikipedia.org/wiki/FOIL_method

    First stated in. 1929; 95 years ago (1929) In elementary algebra, FOIL is a mnemonic for the standard method of multiplying two binomials [1] —hence the method may be referred to as the FOIL method. The word FOIL is an acronym for the four terms of the product: F irst ("first" terms of each binomial are multiplied together) O uter ("outside ...

  9. Multiplication table - Wikipedia

    en.wikipedia.org/wiki/Multiplication_table

    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 ...

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