March_ing with Mathematics!

  •   Sat, Mar 14 2026
  •   By Stephen P D’Souza, Melbourne

March 14, 2026

On March 14, every year, the world celebrates an official International Day dedicated to Maths called the ‘International Day of Mathematics,’ also known by its abbreviation IDM. Formally proclaimed by UNESCO in 2019, it is now observed globally to celebrate the role of mathematics in science, education, culture and everyday life. ‘Mathematics and Hope,’ being the theme for the year 2026, the focus is on how mathematics – like hope – is a universal human asset; it helps us understand reality, make responsible decisions with data, build trust and work together towards solutions for shared challenges.

In this piece of writing, I have curated a few ‘Mathematical Number Wonders’ from my Collection – a fun and creative celebration of Maths! Let’s kick things off with a classic brain-teaser: What is 10,989 x 9? Here’s the magic – just reverse the digits and voila! You get 98,901. That’s the answer! In the few ‘mathematical mystics,’ that follows below, I have referred to the other person as a ‘male friend’ for consistency. So, grab your calculator (or work it out manually), roll up your sleeves and let’s get those brains cracking with numbers!

Merry Milestones:

Who does not like their birthdays to be celebrated? As kids, that was something we always looked forward to. As we grew older, we conveniently forgot the year we were born, but never the date. 

Let us try this ‘birthday and birth month’ trick. Ask your friend to take the day they were born:

  • Multiply by 5. Add 6.
  • Multiply by 4. Add 9.
  • Multiply by 5 again.
  • Finally, ask them to add the day of the month they were born.
  • Subtract the number 165.

The final number will magically reveal their birthday: the first digit/s = day, the last two digit/s = month!

For example: Your friend’s birthday is today, March 14. [14 x 5 = 70; 70 + 6 = 76; 76 x 4 = 304; 304 + 9 = 313; 313 x 5 = 1565; 1565 + 3 = 1568; 1568 – 165 = 1403]. 14 is the day they were born; 03 denotes March, being the 3rd month of the year.

Here is a bit of a variation, guessing one’s age. Ask your friend to think of the:

  • First digit of their age (if under 100).
  • Multiply by 2, then add 5.
  • Multiply by 5 again.
  • Add the second digit of their age.
  • Then subtract 25.

Magically, the result will be their age.

For example: (age 34); First digit = 3; Second digit = 4. [3 x 2 = 6; 6 = 5 = 11; 11 x 5 = 55; 55 + 4 = 59; 59 – 25 = 34]

Mental Magic:

Let’s continue with your age, but clubbed with your house/flat number.

  • Take your house/flat number and double it.
  • Add 5, then multiply everything by 50.
  • Now, sneak in your age (if you’re under 100).
  • Add the number of days of a calendar year.
  • Subtract by 615. 

Ta-da!

The last two digits reveal your age and the rest: digits before them – that’s your house/flat number. Simple Maths – with a sneaky little twist that feels like magic! 

For example: Imagine your house/flat number is 1234 and your age is 67. [1234 + 1264 = 2468; 2468 + 5 = 2473; 2473 x 50 = 123650; 123650 + 67 = 123717 + 365 = 124082; 12082 – 615 = 123467].

Mobile Marvels:

Say this before you begin: ‘I will stretch your telephone number … scramble it … shrink it and still bring it safely back home!’ Then, reveal that the final number must be exactly what they started with.

Here’s a 10-digit mobile number magic trick that works with the entire number at once. Exclude any codes preceding the mobile number.

Ask your friend to secretly take their entire 10-digit phone number and follow these steps:

  • Multiply your phone number by 3.
  • Add 12.
  • Multiply the result by 4.
  • Divide the result by 12.
  • Subtract 4.

The magical result:

They will end up with their 10-digit phone number, no matter what number they start with!

It looks complicated - but their number always comes back unchanged.

For example: Imagine the 10-digit mobile number is 9623147085.

[9623147085x 3 = 28869441255; 28869441255 + 12 = 28869441267; 28869441267 x 4 = 115477765068; 115477765068/12 = 9623147089; 9623147089 – 4 = 9623147085].

Let’s work out the trick with an 8-digit 36512984.

[36512984 x 3 = 109538950; 109538950 + 12 = 109538964; 109538964 x 4 = 438155856; 438155856 / 12 = 36512988; 36512988 – 4 = 36512984].

You can try to see whether it works with other digits. I have taken in the contexts of: Indian mobile numbers of 10 digits and Australian/few Arabian Gulf countries of 8 digits.

Now, let us tweak the trick with the same 10-digit phone number, split into two:

Before you start, dramatically say: “I will rearrange numbers … but your phone number can never escape mathematics!”

Ask your friend to secretly split their 10-digit phone number into:

First 5 digits (call this Part A); Last 5 digits (call this Part B).

Now, guide them through this:

  • Take Part A (first 5 digits)
  • Multiply it by 80. Add 1.
  • Multiply the result by 2500.
  • Add Part B (last 5 digits)
  • Add Part B again. Subtract 2500.
  • Divide everything by 2. 

The final number they get will be … their complete original 10-digit phone number!

Let us take the same mobile number as worked above 96231 47085;

[96231 x 80 = 7698480; 7698480 + 1 = 7698481; 7698481 x 2500 = 19246202500; 19246202500 + 47085 + 47085 = 19246296670; 19246296670 – 2500 = 19246294170; 19246294170/2 = 96231 47085]

Mesmerising Multiple:

My favourite number is 9 simply because it’s my birthdate and my favourite colour is green – algae/olive green would be my preferential shade. 9 is my jersey number and likewise, whichever sportsperson adorns that number jersey is my favourite too – whether he is a good player or not is secondary. In a horse race, I will be rooting for the jockey riding Horse No. 9 and in fancy fete games, I would be putting my bets on No. 9!

Now, let’s try the 9-trick:

Ask your friend to pick any number:

  • Let the picked number be multiplied by 9.
  • Add the digits of the result together.
  • Keep adding the digits until it becomes a single number.
  • No matter what they pick, the answer will always be 9.

For example: The number picked is 657; [657 x 9 = 5913; 5+9+1+3 = 18; 1 + 8 = 9].

Mind Mapping:

Let’s interpret the mind-reading number. Ask your friend to think of a number, say 15.

  • Double it: 15 x 2 = 30
  • Add 8: 30 + 8 = 38.
  • Divide by 4: 38/4 = 9.5
  • Subtract half of the number they originally thought of: 9.5 – 7.5 = 2.

Ta-da!

No matter what number they start with, they’ll always land on 2. Watch their face light up – Maths has never been this sneaky and fun!

Variations of this game can also be had:

Addition of 8 gives 8/4 = 2 as the result.

Similarly, addition of 12, 16, etc. (multiples of 4) will respectively give 12/4, 16/4 i.e. 3, 4 etc., as the outcomes.

Mathematical Missive:

Now, that you have burnt plenty of brain power in the quest to become ‘mathematical wizards,’ to end, here is a little breather - A Letter from Mr Algebra to Mr Calculus …

Mathematical House,

22/7 Diagonal Road,

Near Bisector College,

Numberless State.
 

Dear Mr Calculus, 

Subject: An equation for Matrimonial Harmony 

Greetings from the land of equations and variables! 

I write this with great enthusiasm regarding the proposed unions of my sons: Mr Zero – whose humility balances cosmos and Mr Infinity – whose presence remains boundless, unaltered by any addition or subtraction. They seek the companionship of your daughters: Miss Differentiation – sharp, precise and full of subtle charm and Miss Integration – graceful, all-encompassing and harmoniously complete. 

 

I have consulted Newton’s Third Law of Marriage. “To every marriageable husband, there is an equal and opposite wife.” With this principle, I am confident that these unions are perfectly balanced. In the matter of Mr Infinity, both Mr Formula and Pandit Logarithm have affirmed their eternal constancy. You may, of course, consult Uncle Statistics and Aunt Dynamics for additional insights. Our celebration will be further enhanced by the presence of Alpha, Beta, Gamma, Delta and naturally, the Universal Set. Together, we shall form a gathering as legendary as any theorem. 

Please convey my warmest regards to your sister, Geometry, whose elegance and symmetry we deeply admire. Once the consultations are complete, do feel free to fix a date for this grand matrimonial experiment. 

With mathematical precision and infinite good wishes, 

Yours algebraically,
Algebra

 

 

 
By Stephen P D’Souza, Melbourne
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