Divisibility Tricks

Oct 27, 2009  
Is the number N divisible by.... 2? 3? 5?

Everyone knows the first trick:
N is divisible by 2 if its last digit is 0, 2, 4, 6, or 8 (that is, last digit is even).

Most people know the next trick:
N is divisible by 3 if the sum of the digits is also divisible by 3.
You can repeat this rule too.

For example: Is the number 93,225 is divisible by 3? Well...
9+3+2+2+5 = 21
And, 21 is divisible by 3, hence 93,225 is divisible by 3.
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How to Compute Cubed Roots Fast

Aug 9, 2009  
Take a look at this video of Scott Flansburg on the Discovery Channel's "More Than Human":

Scott Flansburg takes cubed roots fast

In the video you see Scott Flansburg take the cubed root of 658,503 to get an answer of 87 in a matter of a second. How does he do it you ask?
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How to Square 2-digit Numbers Fast

Aug 8, 2009  
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The Human Calculator - Scott Flansburg

Aug 1, 2009  
  • Scott Flansburg was born in New York on December 28, 1963.
  • He served in the U.S. Air Force (1982-1988) and had a tour of duty with the Office of Special Investigations in Tokyo, Japan. He then returned to the United States and became an advocate of teaching math in an innovative fashion. 
  • In 1989 he drew the attention of Regis Philbin. Mr. Philbin is the individual that is credited for naming Scott, The Human Calculator during his appearance on The Regis and Kathy Lee Show. 
  • In 1991 he began working on a project called Turn On the Human Calculator In You, a series of tapes that was subsequently on Mike Levy's Amazing Discoveries.
  • Turn On the Human Calculator In You was one of the most successful early infomercials touted as having in excess of 125 million viewings.
  • The follow-up product was called Mega Math with Kevin Tredeau (1996) which added a video and workbook and was later published by Tru Vantage International.
  • He has subsequently appeared on countless television shows including Oprah, Ellen, The Tonight Show with Jay Leno, Good Morning America, Discovery Channel's `More Than Human', and thousands of local radio and TV shows.
You can take a look at the infomercial here:
amazing discoveries calculator picture
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Speed Math via Vedic Mathematics

Jul 26, 2009  
Vedic mathematics is based on sixteen su-tras which serve as somewhat cryptic instructions for dealing with different mathematical problems. Below is a list of the su-tras, translated from Sanskrit into English. They were presented by a Hindu scholar and mathematician, Jagadguru Swami Sri Bharati Krishna Tirthaji Maharaja, during the early part of the 20th century.

  1. By one more than the previous one
  2. All from 9 and the last from 10
  3. Vertically and crosswise (multiplications)
  4. Transpose and apply
  5. Transpose and adjust (the coefficient)
  6. If the Samuccaya is the same (on both sides of the equation, then) that Samuccaya is (equal to) zero
  7. By the Para-vartya rule 
  8. If one is in ratio, the other one is zero.
  9. By addition and by subtraction.
  10. By the completion or non-completion (of the square, the cube, the fourth power, etc.)
  11. Differential calculus
  12. By the deficiency
  13. Specific and general
  14. The remainders by the last digit
  15. The ultimate (binomial) and twice the penultimate (binomial) (equals zero)
  16. Only the last terms
  17. By one less than the one before
  18. The product of the sum
  19. All the multipliers
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The Trachtenberg Speed System

Jul 25, 2009  
Who was Trachtenberg?

  • Professor Jakow Trachtenberg was the founder of the Mathematical Institute in Zurich, Switzerland.
  • He was a Russian, born June 17th, 1888 and studied engineering.
  • While still in his early twenties, he became Chief Engineer with 11,000 men under his supervision.
  • After the Czar of Russia was overthrown, he escaped to Germany where he became very critical of Hitler. He was later imprisoned.
  • Most fellow prisoners around him gave up hope and died even before being sent to their death. He realized that if he wanted to stay alive, he had to occupy his mind with something else rather than focus on the hopeless conditions surrounding them. He set his mind on developing methods to perform speed mathematics.
  • With the help of his wife, he escaped from prison and fled to Switzerland.
  • There, he taught his speed math system to young children. It was very successful.
Trachtenberg developed a set of rules (algorithms) to multiply long numbers by numbers from 0 to 12. These rules allow one to dispense with memorizing multiplication tables, if that is desired.
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