What’s your favorite equation?
It has been a while since we had a survey on any mathematics topic, so today I’d like to kick one off. What’s your favorite equation, formula, identity or inequality?
Try to keep it to your top 5 so that things don’t get out of hand – but please share which equation, formula, identity or inequality amuse you the most.
So – What’s your favorite equation, formula, identity or inequality in mathematics and if possible tell us why? Over to you!
Take into consideration all the branches of mathematics
Popularity: 8%
Mathematics of Lord Bramah
Alike Vedas which is the primary source of Vedic Mathematics, mathematics is also extensively used in Indian Mythology. I have picked up a very interesting story related to the creator of universe, Lord Bramah. The story is narrated in the word of the original author -
"In the great temple at Benares, beneath the dome which marks the center of the world, rests a brass plate in which are fixed three diamond needles, each a cubit high and as thick as the body of a bee. On one of these needles, at the creation, God placed sixty-four disks of pure gold, the largest disk resting on the brass plate, and the others getting smaller and smaller up to the top one. This is the Tower of Bramah.
Day and night unceasingly the priests transfer the disks from one diamond needle to another according to the fixed and immutable laws of Bramah, which require that the priest on duty must not move more than one disk at a time and that he must place this disk on a needle so that there is no smaller disk beneath it. When the sixty-four disks shall have been thus transferred from the needle on which at the creation God placed them to one of the other needles, tower, temple, and Brahmins alike will crumble into dust, and with a thunderclap the world will vanish."
The above tower will look something similar to the figure shown below
Now friends it's up to you to find out the time which the priests will take to complete the task.
By the way this world's end prophecy is one of the most optimistic on record!
Popularity: 40%
Ramanujan Number
When you love mathematics you can see magic in numbers. Your face gets lit up when you observe something new about a number. Something similar and very interesting happened with great Indian mathematician
Srinivasa Iyengar Ramanujan
You can see the title of this post is Ramanujan Number. You might have already guessed that he might have a stumbled up on some very interesting number with some peculiar characteristics. If you have guessed that, you are right. Ramanujan number is 1729.
1729 is also known as the Hardy – Ramanujan number . This number is also called the Taxicab number.
Ramanujan number is so named after a famous anecdote of the British mathematician G. H. Hardy regarding a hospital visit to the Indian mathematician Srinivasa Ramanujan.
In Hardy's own words:
“I remember once going to see him when he was ill at Putney. I had ridden in taxi cab number...
Popularity: 54%
Sale Price, Gross Margin determination – Simple Trick
I am going to share with you one trick which one great teacher, Mr S.K. Jha taught me. Simple arithmetical problems of
Finding out selling price, when cost price and margin (percentage of profit on Sale) are given. Or,
Finding out cost price when Sale price is given and percentage of profit on cost is given.
Finding out the mark-up when cost price and Sale price are given.
We all have seen occurrence of such problems in our academic life and day-to-day life. All the time we need a paper – pen or a calculator. But now with the process given below I believe we can solve any such problem in our mind.
Popularity: 38%
Which Day of the Week was My Birthday?
Find the answer to these questions instantly using the simple trick given below -
How to find the day of the week on which your birthday will fall next year?
or,
Which day of week was my birthday last year?
Today it is my birthday and somehow I was curious to know the day of the week on which I was born. Using Microsoft excel I found out that it was Thursday. I also tried listing the day of the week for all my birthdays till I will be 100 years old. I noticed a very simple but interesting facts about the days on which our birthday falls.
Every year the day advances by one day from previous year. For example I was born on 5th April 1984, Thursday. On my first birthday that is on 5yh April, 1985 it will be Friday.
But on every leap year it advances by 2 days. To understand this please refer the table below -
| Date | Day |
| 5-Apr-84 | Thursday |
| 5-Apr-85 | Friday |
| 5-Apr-86 | Saturday |
| 5-Apr-87 | Sunday |
| 5-Apr-88 | Tuesday |
| 5-Apr-89 | Wednesday |
| 5-Apr-90 | Thursday |
| 5-Apr-91 | Friday |
| 5-Apr-92 | Sunday |
| 5-Apr-93 | Monday |
| 5-Apr-94 | Tuesday |
| 5-Apr-95 | Wednesday |
| 5-Apr-96 | Friday |
As per the above table, you can see from year 1984 to 1987, every year the days were advancing by one day. But from 1987 to 1988 (leap), increased by 2 days. Then again it from 1988 to 1991 it increases by one day each year.
So with above logic, now if any one ask me what day was it on my last (2009) birthday, if this year (2010) my birthday is on Monday. It’s very simple, it was Sunday. And next year (2011) it will be Monday. After that (2012 – leap year) it will be Wednesday as on a leap year it will increase by 2 days.
If you have any special observation, please share below -
Popularity: 28%
Cyclic Number
There is a very interesting concept called Cyclic Number.
Cyclic Numbers can be defined as a number with n digits, which, when multiplied by 1, 2, 3, ..., n produces the same digits in a different order.
There are few very famous cyclic numbers. We have given a puzzle question below, if you could answer the puzzle your concept of cyclic number will be crystal clear. That's the reason we have not given example for cyclic numbers.
Can you find a number which added to itself one or several times will give a total having the same digits as that number but differently and after the sixth addition will give a total of all nines?
Leave your answers below. We will provide the answer if you ask for 
Popularity: 11%
Ancient Indian Mathematicians and Their Teachings
Ancient Indian Mathematicians and Their Teachings
We are starting a very special series “Teaching of Indian Mathematicians”.
In this special series we will discuss various concepts propounded by Indian mathematicians which are very useful even today.
Formula for cyclic quadrilateral propounded by 9th Century Indian Mathematician Mahavira
First in this series, I am explaining a very nice concept propounded by Mahavira, a 9th-century Indian mathematician from Gulbarga (South India) who asserted that the square root of a negative number
Popularity: 19%
Why is 1 not a Prime Number?
Is 1 a Prime Number?
Friends, in one of the post where I have described ‘Prime’ and ‘Composite’ Numbers, one of the curious visitor have asked me a very logical question. I will quote that question for your reference –
Text from Previous post-
“Prime and Composite : Any integer which is divisible by 1 and itself only is called a prime number.
unquote
quote
N.B.: 1 is not a prime number.”
Question
Could you explaine what is the creteria thar excludes 1 from the list of prime numbers?
a) 1 is integer
b) 1 is divisible by 1 and itself (1)
Since anybody in the past has declared that 1 is not prime number, why we should follow this without thinking and contravene the general rule for prime numbers?
Is 1 as a figure is something which has come from the thin air. It is and always will be an integer. The criteria for 2 are the same – divisible by 1 and itself. And for all prime numbers.
Most probably the 1 is “guilty” because with 1 starts the series on numbers (natural, odd or prime). Suppose 2 was the beginning of the series. Should we ignore 2, because series starts with 2?
Popularity: 10%
Comparison of Fractions
Comparison of fractions: Suppose, some fractions are to be arranged in ascending or descending order of magnitude.
Popularity: 11%
Decimal Fraction Rules
Multiplication of a decimal Fraction by a Power of 10: Rule: Shift the decimal point to the right by as many places of decimal as is the power of 10.
Multiplication of Decimal fractions:- Rule :- Multiply the given numbers considering them without the decimal point. Now, in the product, the decimal point is marked off to obtain as many places of decimal as is the sum of the number of decimal in the given numbers.
Dividing a Decimal fraction By a Counting Number
Rule: - Divide the given number without considering the decimal point by the given counting number. Now, in the quotient, put the decimal point to give as many places of decimal as are there in the dividend.
Popularity: 13%
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