Secrets of Mental Math
Last night I started reading ‘Secrets of Mental Math‘ by Michael Shermer and Arthur Benjamin, a book packed full of Mental Maths Hacks.
Even before the first chapter had ended, ‘Secrets of Mental Math‘ left me wondering why I hadn’t been taught to calculate simple maths like this at Primary School. Excited by such geekery, that I had to share a couple of examples from the book.
The books commences with the old Mental Mathmagician standard of instantly calculating a multiple of 11.
For instance
34 x 11
Shermer and Benjamin’s method is to take the first digit of the first number (3) and add it to the second digit (4), then take the outcome (7) and set it between the first and second digit of the first number resulting in an answer of 347.
Things get a little more complicated (but not a lot) if the the first and second digit of the first number result in an number above 9. Take 78 x 11 for example, the outcome of 7 + 8 is 15 which by using our previous method would mean the answer to 78 x 11 is 7158, which is obviously wrong. To get the correct answer we simply select the 1 from 15 and add and add it to the first digit of 78 so it becomes 88. That done, we carry on as before by taking the remaining 5 and inserting it between 88 to give an answer of 858.
This little Maths hack is just the tip of the Iceberg. Shermer and Benjamin take you through a program which allows the computation of any Addition, Substraction, Multiplication, Division, Square Root or fraction mentally.
Have a look at what else I’m reading by visiting Readernaut.