The Magic of Number 9 (Part 1)
Have you ever noticed that the number 9 is kind of amazing? What's that…did I hear you say "NO?" Then prepare yourself to be amazed and keep on reading to learn all about the magic behind the mysterious number 9
By Math Dude Jason Marshall
Scientific American presentsMath DudebyQuick & Dirty Tips. Scientific American and Quick & Dirty Tips are both Macmillan companies.
After our3 frequently asked questions about math puzzlesepisode last week, math fan Cynthia wrote to tell me about one of her favorite puzzles. As luck would have it, Cynthia's puzzle is based upon one of the same ideas that—as we'll soon find out—makes our as-yet-unexplained third-and-final puzzle from last time tick.
What's the tie-in between the two? As we'll see, they're both based upon some pretty amazing properties of the mysterious and sometimes seemingly magical number 9. How does it all work? And what makes the number 9 so "magical?" Those are exactly the questions we'll be answering over the next few weeks!
A Mathemagical Trick
Before we get to those amazing properties of the number 9, I want tostart by telling you about the mathemagical trick that math fan Cynthia sent me. This is definitely one that you'll want to play along with. Here's how it goes:
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Start by thinking of a number, any number.
Now, multiply that number by 9.
If the result isa multi-digit number, add its digits together to come up with a new number.
If that new number is still a multi-digit number, add its digits together to come up with yet another new number. Continue doing this until you end up with a 1-digit number.
Once you have a 1-digit number, subtract 5 from it.
Now, using the standard numbering of the English alphabet (where 1 is A, 2 is B, and so on), find the letter corresponding to your number.
Next, think of a European country that begins with that letter.
Then take the last letter of that country and think of an animal that begins with that letter.
Finally, take the last letter of that animal and think of a color that begins with that letter.
Okay, now—oh, wait a minute—you do know that there aren't any orange kangaroos in Denmark, right?
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FAQs
A Mathemagical Trick
What is the magic behind the number 9? ›
It is the highest single-digit number, and any number multiplied by 9 will always result in a number whose digits add up to 9. Additionally, the number 9 is the sum of the first three square numbers (1² + 2² + 3² = 9) and the sum of the first three cube numbers (1³ + 2³ + 3³ = 36).
What does the number 9 symbolize? ›
The meaning of the number 9
In numerology, the number 9 is powerful. It represents completion, although not a final ending—more like the fulfillment of one cycle so that you can prepare to initiate the next one.
What is the magic number of 9? ›
9 is a Motzkin number, for the number of ways of drawing non-intersecting chords between four points on a circle. Four concentric magic circles with 9 in the center (by Yang Hui), where numbers on each circle and diameter around the center generate a magic sum of 138. magic square has a magic constant of 369.
What is the trick for multiplication of 9? ›
The rule is when you multiply any number with 9, then the left part of the answer is the result of operation of “original number – number formed by ignoring the one's place digit – 1”, and the right part is the one's place digit of the result of multiplication of one's place digit of original number with 9.
What is the magic number 9 trick? ›
A Mathemagical Trick
Start by thinking of a number, any number. Now, multiply that number by 9. If the result is a multi-digit number, add its digits together to come up with a new number. If that new number is still a multi-digit number, add its digits together to come up with yet another new number.
Is the number 9 good or bad? ›
We can say that Number 9 is a fortunate number as this number brings a prosperity, happiness and good luck in life. Number 9 is associated with Mars and its a powerful number but the people who are born on the dates 9, 18, 27 have an aggression issue as they easily get angry on small things.
Is 9 a perfect number? ›
Is 9 a Perfect Number? No, 9 is not a perfect number because its factors (1 and 3) excluding 9 do not sum up to 9. They sum up to 4. And we know that the sum of the factors of Perfect numbers is always the number itself.
Does the number 9 exist? ›
Nine is a natural number in the number system. This is an odd number. 9 is also a composite number (not a prime number). Nine is even the sum of the first three consecutive odd numbers in the number system: 1, 3, and 5 ( 1 + 3 + 5 = 9).
How do you multiply by 9 mentally? ›
To multiply any number by 9, simply subtract one from the number you are multiplying and the answer will be the first digit. The second digit will be the difference between 9 and the first digit. For example, to multiply 8 by 9, subtract one from 8, which is 7.
Divisibility Rule of 9
The rule for divisibility by 9 is similar to divisibility rule for 3. That is, if the sum of digits of the number is divisible by 9, then the number itself is divisible by 9.
What is unique about number 9? ›
Number '9' is a square of 3. Any natural number having sum '9' or multiple of '9' is always divisible by '9'. '9′ is the largest single digit number and also any largest number like largest 2 digit no. (99) largest 4-digit no.
What secret is number 9 in numerology? ›
As number 9 is the last in the series of single-digit numbers, it conveys fulfilment, and is also considered particularly mystic. Those with the personality number 9 may be perceived as artists. You're sure to be successful in any kind of creative occupation, especially music and singing.
What does the life path number 9 mean spiritually? ›
Being a life path 9 means embarking on a lifelong quest to quench an insatiable thirst for growth and new experiences. “Life path 9 people are always searching for more: more experiences, more education, more deep talks, and the next adventure,” numerologist Jasmine Wolfe tells Bustle.
What is the magic number of the universe? ›
The Fine-structure Constant: A Cosmic Clue
To the world of physics, 137 is synonymous with the fine structure constant. This constant, represented as approximately 1/137.03599913, gauges the strength of the electromagnetic force, according to the National Institute of Standards and Technology.
