Magic wIth Math

By Rajinder Goswami

Magic with Math is a book to solve mathematical problems with magical speed that surprise all. It is useful for students starting from 5th standard up to all competitive exams .This book is best for Quantitative Aptitude. The book is about basics and fundamentals of mathematics. The methods told in this book are based on practical experience of the author and Some of the methods are not given in any other book. The fundamentals and basics are explained with clear logic to make the students to understand and grasp the topics. The author hates cramming and rote learning. The mainly helps to improve your calculating speed.

• Language: English
• Publisher: Rajinder Goswami
• Release date: Jan 17, 2015
• ISBN: 9781310608773

Rajinder Goswami

Basically I am a Banker having great interest in numbers and mathematics. I have developed many shortcuts and calculation enhancing tactics especially for Quantitative Aptitude Tests. I am a Bachelor in Commerce and post graduate in Economics and have also secured a professional degree in Banking. I got voluntary retirement for the Banking and opened my coaching center where I am fulfilling my passion for teaching. I am giving coaching for all competitive classes.

Book preview

Addition and Subtraction

Practically we are more comfortable with doing addition than doing subtraction. Addition is easier. Even computers and calculators don’t know how to subtract! These two most advanced calculating gadgets only know Addition and they perform subtraction with the help of addition.

Even an illiterate shopkeeper (who doesn't use a calculator) applies this method of addition for doing subtraction. In fact, addition is a natural way of doing subtraction.

Suppose I purchased certain grocery items from the grocer. He made the bill amounting to be $337. I handed over $500/- note to him.

He will hand over the grocery items to me and says:

•I have given you $337.(Value of grocery)

•"Take $3. You have $340 now. (337+3=340)

•Take $10 more, you have 350. (340+10=350)

•"Take $50 and now you have $400. (350+50=400)

•"Take $100 and you have $500. (400+100=500)

So, he has returned me 3+10+50+100=$163 in all in cash along with grocery worth $337.

Mind it. The grocer has not used subtraction. He has smartly used his Adding Skill to reach the amount to be paid back to me. (500–337=163).

This method is generally not discussed in the books. One of my colleagues taught me this method when I was working in a Bank. With continued practice I realized that this method is really fast and seldom leads to any error,

We can apply this method with ease while doing any subtraction. Perhaps, initially, this method may irritate you, but in the long run this is the best way of doing subtraction. With a little patience and continuous practice you will also feel comfortable with this once you master this.

Let’s start with a very simple example:

Subtract 65463 from 97894

So, 98894-65463=32431

Please note: We have not subtracted. We have used the operator ‘+’ to do subtraction.

But it was a very simple example where 'carry-overs' were not involved. Now let’s take one tougher example with 'carry-overs' which are invariably present in the subtraction problems.

We want to subtract 39648 from 75062

In the similar way we can do all the subtraction sums with the help of addition. Just a little more practice will make you comfortable with this system. Believe me, it is easier and gives more accurate results.

Now let’s do another sum where we can easily use ‘+’ operator to reduce our calculation time:

45026+125648 +9487+? = 687048

In such type of sums, we usually add the numbers on the left hand side and then deduct this sum from the number on the right hand side to arrive at the requisite answer.

By doing so, we will be making two different calculations. First, finding out the sum of the figures on the left hand side and then deducting the same from the right hand side. We can solve this sum it in a different way as illustrated below:

Dear student, there is an old saying, If you look at a problem from a different angle, it is also an invention.

So try to see the problem in hand from a different prospective. There is always a scope to do the same job in a much better way. All the best gadgets available in the market today will be improved upon in the near future. There is always a scope for improvement. So try to find out better and easier ways for doing calculations also. If you try it out, you will certainly discover one new method for you.

Subtraction in case of all trailing zeros

It is still easier to find subtraction when we encounter all the trailing zeros.

Suppose we want to subtract 2,456,015 from 740,000,000

Deduct 22,456,983 from 540,000,000

Deduct 54,109 from 5,000,000

Adding two numbers of two digits

Add 56 and 97

Now try calculating 79+48:

With a little practice, you will be able add such numbers mentally.

70+40 =110 and 9+8=17

So 110+17=127

Try these doing mentally: