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  2. 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.

  3. Mike Byster - Wikipedia

    en.wikipedia.org/wiki/Mike_Byster

    Michael Byster (born March 5, 1959) is an American mental calculator, and math educator. He worked as a commodity trader until he quit his job to devote himself to teaching children his methods. He has spoken to over 10,000 classrooms for free and continues to mentor children.

  4. Trachtenberg system - Wikipedia

    en.wikipedia.org/wiki/Trachtenberg_system

    Subtract the right-most digit from 10. Subtract the remaining digits from 9. Add the neighbor to the sum; For the leading zero, subtract 1 from the neighbor. For rules 9, 8, 4, and 3 only the first digit is subtracted from 10. After that each digit is subtracted from nine instead. Example: 2,130 × 9 = 19,170 Working from right to left:

  5. These Calculators Make Quick Work of Standard Math ... - AOL

    www.aol.com/best-calculators-students...

    These Calculators Make Quick Work of Standard Math, Accounting Problems, and Complex Equations. Stephen Slaybaugh, Danny Perez, Alex Rennie. May 21, 2024 at 2:44 PM.

  6. Mental abacus - Wikipedia

    en.wikipedia.org/wiki/Mental_abacus

    This article about a number is a stub. You can help Wikipedia by expanding it.

  7. Chisanbop - Wikipedia

    en.wikipedia.org/wiki/Chisanbop

    36 represented in chisanbop, where four fingers and a thumb are touching the table and the rest of the digits are raised. The three fingers on the left hand represent 10+10+10 = 30; the thumb and one finger on the right hand represent 5+1=6. Counting from 1 to 20 in Chisanbop. Each finger has a value of one, while the thumb has a value of five.

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  9. Mnemonics in trigonometry - Wikipedia

    en.wikipedia.org/wiki/Mnemonics_in_trigonometry

    Signs of trigonometric functions in each quadrant. All Students Take Calculus is a mnemonic for the sign of each trigonometric functions in each quadrant of the plane. The letters ASTC signify which of the trigonometric functions are positive, starting in the top right 1st quadrant and moving counterclockwise through quadrants 2 to 4.