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  2. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    The product of two variables ranging from 90-99 will result in a 4-digit number. The first step is to find the ones-digit and the tens digit. Subtract both variables from 100 which will result in 2 one-digit number. The product of the 2 one-digit numbers will be the last two digits of one's final product.

  3. Product (mathematics) - Wikipedia

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

    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).

  4. Elementary arithmetic - Wikipedia

    en.wikipedia.org/wiki/Elementary_arithmetic

    [7] [8] The sum of two numbers is unique; there is only one correct answer for a sums. [8] When the sum of a pair of digits results in a two-digit number, the "tens" digit is referred to as the "carry digit". [9] In elementary arithmetic, students typically learn to add whole numbers and may also learn about topics such as negative numbers and ...

  5. Multiplication - Wikipedia

    en.wikipedia.org/wiki/Multiplication

    For example, 4 multiplied by 3, often written as and spoken as "3 times 4", can be calculated by adding 3 copies of 4 together: 3 × 4 = 4 + 4 + 4 = 12. {\displaystyle 3\times 4=4+4+4=12.} Here, 3 (the multiplier ) and 4 (the multiplicand ) are the factors , and 12 is the product .

  6. Persistence of a number - Wikipedia

    en.wikipedia.org/wiki/Persistence_of_a_number

    The additive persistence of 2718 is 2: first we find that 2 + 7 + 1 + 8 = 18, and then that 1 + 8 = 9. The multiplicative persistence of 39 is 3, because it takes three steps to reduce 39 to a single digit: 39 → 27 → 14 → 4. Also, 39 is the smallest number of multiplicative persistence 3.

  7. Karatsuba algorithm - Wikipedia

    en.wikipedia.org/wiki/Karatsuba_algorithm

    The Karatsuba algorithm is a fast multiplication algorithm. It was discovered by Anatoly Karatsuba in 1960 and published in 1962. [1][2][3] It is a divide-and-conquer algorithm that reduces the multiplication of two n -digit numbers to three multiplications of n /2-digit numbers and, by repeating this reduction, to at most single-digit ...

  8. Perfect number - Wikipedia

    en.wikipedia.org/wiki/Perfect_number

    For instance, 6 has proper divisors 1, 2 and 3, and 1 + 2 + 3 = 6, so 6 is a perfect number. The next perfect number is 28, since 1 + 2 + 4 + 7 + 14 = 28. The first four perfect numbers are 6, 28, 496 and 8128. [1] The sum of proper divisors of a number is called its aliquot sum, so a perfect number is one that is equal to its aliquot sum.

  9. Kaprekar's routine - Wikipedia

    en.wikipedia.org/wiki/Kaprekar's_routine

    As an example, starting with the number 8991 in base 10: 9981 – 1899 = 8082 8820 – 0288 = 8532 8532 – 2358 = 6174 7641 – 1467 = 6174. 6174, known as Kaprekar's constant, is a fixed point of this algorithm. Any four-digit number (in base 10) with at least two distinct digits will reach 6174 within seven iterations. [1]