Tag Archives: CHRISTmaths

The 12 Problems of CHRISTmaths

Vintage Christmas—Just like Baby Jesus two millennia ago!
Vintage Christmas—Just like Baby Jesus two millennia ago!

Christmas is a golden and joyful opportunity for number enthusiasts and math geeks to sharpen their creative mathematical problem-solving skills.

Here are 12 CHRISTmaths cookies that may help you shake your brain a little bit in the midst of Christmas festivities.

Warning: Refrain from forwarding this post to relatives or friends living in countries, which are intolerant of Christmas and Christianity, such as Brunei, Saudi Arabia, and Somalia, as it’s haram for “infidels” to take part in any kind of Christmas celebrations. And I assume that includes reading any on-line materials deemed un-Islamic or un-Mohammedan, which might lead believers astray from the faith.

1. Unlucky Turkeys

Estimate the number of turkeys that make their way to the supermarkets every year.

2. A Xmas Candy

Mary wanted to buy a candy that costs 25 cents. A dated vending machine would take one-cent, five-cent, and ten-cent coins in any combination. How many different ways can she use the coins to pay for the candy?

Christmastize your code!
Remember to scan your Christmas item!

3. The Dimensions of a  Cross

A square of side 25 cm has four of its corners cut off to form a cross. What is the perimeter of the cross?

4. The Number of Crossings

Two lines can cross one time, three lines three times, four lines six times, and five lines ten times. If there are 25 lines, what would be the maximum number of crossings be?

5. An Eco-Xmas

If all instances of the word “CHRISTMAS” were replaced with “XMAS,” how much ink and paper (or Xmas trees) could you save every year? How much money could be channelled back to feeding the poor and the hungry during the festive season?

XMaths Tech
© T. Gauld’s You’re all just jealous of my jetpack (2013)

6. Number of Xmas Cards

In an age of Xmas e-cards and video cards, how many Christmas greetings cards are still being sent worldwide? How many trees are being saved every festive season?

7. Does Xmas! have 25 digits?

1! = 1, 2! = 1 × 2 = 2, 5! = 1 × 2 × 3 × 4 × 5 = 120—a 3-digit number, and 10! = 1 × 2 ×⋯× 10 = 3,628,800—a 7-digit number.

(a) Without a calculator, how would you verify whether the number 25! has precisely 25 digits or not.

(b) Which positive integers n (other than the trivial case n = 1) for which n! has exactly n digits?

GST with no thanks to Father Xmas
GST (or VAT) with no thanks to Father Xmas

8. Xmas Trees

Guesstimate how big a forest would 25 million Christmas trees occupy.

9. Folding papers

Fold a single piece of paper perfectly in half, from left to right. How many creases will there be after the 25th fold, when you continue folding so that all the rectangles are folded into two halves each time?

10. Pre-Xmas Tax

Imagine Singapore were to implement a pre-Christmas tax on all kinds of Christmas marketing before the first week of December. Estimate how many extra million dollars would the Income Tax department collect every festive season.

Folding a Santa Claus
© Anonymous Folding a Santa Claus

11. A Xmas Quickie or Toughie

What is the sum of the last two digits of 1! + 2! + 3! +⋯+ 24! + 25!?

12. An Ever-Early Xmas

Show that as one celebrates more and more Christmases (or, as one gets older and wiser), Christmas seems to come earlier every year.

Xmas Möbius Strips
Christmas Möbius Strips


Gould T. (2013). You’re all just jealous of my jetpack. New York: Drawn & Quarterly.

Yan, K.C. (2011). Christmaths: A creative problem solving math book. Singapore: MathPlus Publishing.

Zettwoch, D., Huizenga, J., May, T. & Weaver, R. (2013). Amazing facts… & beyond! with Leon Beyond. Minneapolis: Uncivilized Books.

A Xmas Bonus: 25 CHRISTmaths Toughies from Singapore ?? http://tinyurl.com/q9w3ne9


Selected Hints & Answers

2. 12 ways. Hint: Make an organized list.

3. 100 cm. 

4. 300 crossings.

5. About 30 million gallons of ink, 500 square miles of paper, and $15 trillion could be saved.

6. Hint.

7. (b) n = 22, 23, 24.

9. 225 – 1.

11. 4.

12. Hint: Why as one gets older, time appears to fly faster.

2012-12-21 23.13.28

© Yan Kow Cheong, December 25, 2015.


17 Theomatical Haikus for Math Educators

Composing some Theomatics-related haikus may prove therapeutic for stressful math educators, who are prone to overusing their left part of the brain. Why not let these 17-syllabled verses reactivate some atrophied part of your grey matter? Who knows? This right-brained activity may indirectly help rekindle your mathematical creativity!

The Trinity

The True Living God
Ever Three and ever One
A mystery, indeed!

Christ And Mathematics Education (C.A.M.E)

Come to worship Him
Christ and math education

Theomatics, Anyone?

Teach math Christianly 
As an act of true worship
It sure honors Him


Two Conference Proceedings of the Association of Christians in the Mathematical Sciences (ACMS)

Pi in the Sky

The Biblical pi
Is a rational number
From the Book of Kings

π = 3.14 and John 3:16

So close, yet so far
Rational and eternal
The union is null.

The X-tian Pi

The true Christian life
Is like the contextual pi
Constantly changing


The molten sea as described in 1 Kings 7:23. © The Golem Press


Learning math with God
It’s time to take up your cross
To shake up your brain



A Divine Paradox

100 percent man
And 100 percent God, too
What a paradox!

God’s Nature

The nature of God
1 + 1 + 1 (mod 2)
Same, yet different

The Most Quoted Verse

What’s John 3:16?
God’s numerical message
Of His Love for us


A treat for the mind, the eyes, and the spirit


Singapore Math

The Model Method
A blessed strategy
For problem solvers


A little red dot
Has blessed math educators
From all walks of life

Our Servant Math

In one God we serve
May His Spirit guide us
To make math serve us

The Mathematical Book of Life

Conjectures and Proofs
The Great Mathematician
Will bless you with both


2 Kings 3:16 Calligraphy by Andrzej Kot (Poland)

What’s Prayer?

When illogic reigns
When 1 + 1 is not 2
When naught can be one

One Life, Two Unions

One plus one is one.
Then, one plus one turns to 3.
One plus one turns nought.

Primes & Priests

Both are hard to find.
They hold the key to success.
Have faith in them both!


Calligraphy by Hermann Zapf (Germany)



Yan, K. C. (2011). Mathematical haikus for Kiasuswww.singaporemathplus.com

© Yan Kow Cheong, May 18, 2013.