Alabi Stephen - Mentally Calculate It: Gateways To Becoming A Human Calculator

INTRODUCTION

I cannot describe in words how excited I was the day I first saw how to multiply any two-digit number by the number 11 faster than a calculator. Let me show you. Lets take for instance I wish to multiply 53 by 11. It is as easy as adding the digits of the two-digit number together and dropping it in their middle. So 5+3=8, and the answer to 5311 has to be 583. Impressive, isnt it?

This little trick or call it shortcut was what turned me to a math nut and as James Randi said, Immunization against such afflictions are not available. You have to recover all by yourself. Beware. After learning the trick, the next thing I learned was how to square any number that ends in 5 faster and some other mind blowing magical feats.

My curiosity to know more soon overcame me and it became so unbearable until I delve into the world of studying numbers and the beautiful pattern they are capable of displaying. In the middle of my ardent quest to find out better and faster way of computing and calculating numbers, I came across one of the most important person in my life. He is my distant teacher and a professor of mathematics at Harvey Mudd College, Claremont, California. He is my greatest discovery outside of my relationship with God. He is the brain behind most of the procedures and processes laid out in this book and most mathemagic tricks of today. He popularized the term mathemagician. He is a mathematics teacher and of course a mathematics entertainer better known as a mathemagician. He is Professor Arthur Benjamin. I read two of his books secrets of mental math and the magic of math. I also watched a lot of his videos and from there I learnt most of the shortcuts for doing mental math as presented to you in this book. This is why I dont see myself as a genius or a prodigy because what I can do, I learnt from someone, and if anyone also cares enough to learn the way it is done and put in a lot of effort and practice, he would do exactly what Im doing with relatively the same speed or even faster.

This book will show you how to round a few of the corners and cut through some of the traffic while dealing with arithmetic. One of the things that dawned on me while studying most of the mental math shortcuts was as I worked through the shortcuts I could see other ways of calculating faster and easier and with just a little bit of effort I could discover or even create new methods of my own which adds more excitements to my journey through this corner of the world of numbers.

The book is titled: Mentally calculate it gateways to becoming a human calculator. But I must warn that the shortcuts for doing mental math provided in this book are not primarily intended to replace the electronic calculator. I strongly believe there is a place for both. For long and complicated computations, the calculator has no equal, but for some simpler problems, a rapid mental calculation can often give the answer correctly faster than you can enter the function on a calculator. The aim of this book therefore is to lower your dependence on calculator and enhance your self-confidence at using your God-given devices (the mind and the brain) to compute simpler problems. It is therefore my deepest hope that this book will assist towards a better understanding of the basics involved and a deeper appreciation of the wonders of playing with and manipulating numbers.

ALABI STEPHEN

CHAPTER ONE: MENTAL ADDITIONS AND SUBTRACTIONS

L EFT TO RIGHT ADDITION

We pronounce numbers form left to right, we write numbers from left to right and wouldnt it be natural if we could learn to calculate numbers from left to right instead of the right to left method which we were taught in school. When you use the left to right method for arithmetical calculations, youll find out that you can call out your answer before your classmates can put down their pencils on paper. And you dont even need a pencil!

In this chapter youll learn the left to right method of doing mental addition and subtraction for most numbers ranging from two digit to three digit; to even four digit numbers and above with lightning speed.

Why use the left to right method for Arithmetical Operations?

1.The first reason is that to do mental math, the best method suitable for doing it is the left to right way. The right to left method may be good or even best on paper but if you really want to do mental math you have to master your calculations from left to right.

2.The second reason is that doing calculations from left to right gives you a possible and realistic estimate of the answer to your problem. What I mean is, its best to know that your answer is a little over 7500 than to know that it ends in 6. Thus, by working from left to right you begin with the most significant digits in your problem.

3.The third reason for doing calculations from left to right (which is why I love it) is because it gives you the opportunity of saying your answer while youre still calculating in your head.It makes you look like a genius without really trying. To most people it will be like you instantaneously blotted out the answer as soon as you were given the problem.

Given these three reasons, the earlier you get used to computing from left to right, the better.

TWO DIGIT ADDITIONS

The assumption here is that you already know how to add and subtract one digit numbers. We will begin with two digit additions. Also in this chapter youll learn how to simplify your problems by breaking it into smaller, more manageable parts. Also two digit addition can be so easy when it doesnt involve a carry.

For example:

To solve 36 + 23, first add 20, then add 3, after adding 20, you have the problem 56 +3, which equals to 59. It can be illustrated as follows;