SecretsOfMentalMath

Secrets of Mental Math (Arthur Benjamin and Michael Shermer)

  • Great book! Wish I learned it when I was younger.
  • Mental addition and subtraction: Summary, "Left to right"
  • I do not try to see the numbers in my mind – I try to hear them. At each step I hear a new addition problem.
  • For mental addition: it doest matter which number you choose to break up, but it is good to be consistent.
  • Compliments is a nifty technique that will make many three-digit subtraction problems easier to do.
  • Squaring numbers in your head is one of the easiest and yet most impressive feats of mental calculation you can do.
  • In 2x2 multiplication, it often pays to break up the larger number, even if it has the larger last digit. (Unless one of the numbers is in the 50s. then break that number up.)
  • Factoring is my favorite method of multiplying two digit numbers since it involves no addition or subtraction at all. (Factoring is usually easier on your memory) Definitely worth doing when one number is a factor of 11
  • Memorize: 1/6 = 0.1666666… 5/6 = 0.8333333… 1/8 = 0.125 3/8 = 0.375 5/8 = 0.625 7/8 = 0.875 1/11 = 0.09090909… 2/11 = 2x(0.090909…) …. same for the others

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