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 2023-12-08 
In November, I spent some time (with help from TD) designing this year's Chalkdust puzzle Christmas card.
The card looks boring at first glance, but contains 10 puzzles. By colouring in the answers to the puzzles on the front of the card in the colours given (each answer appears four time), you will reveal a Christmas themed picture.
If you're in the UK and want some copies of the card to send to your maths-loving friends, you can order them at mscroggs.co.uk/cards.
If you want to try the card yourself, you can download this printable A4 pdf. Alternatively, you can find the puzzles below and type the answers in the boxes. The answers will automatically be found and coloured in...
13 36 8 13 32 34 18 18 81 81 32 7 11 1 20 40 75 12 94 36 2 2 11 20 7 1 34 11 10 18 64 88 94 60 94 64 94 88 88 60 88 64 2 64 43 2 43 40 49 49 12 60 75 10 49 32 81 18 49 20 34 36 32 40 75 12 43 40 43 12 60 75 36 34 4 11 20 7 10 10 8 7 13 13 4 8 8 1 4 4 1 81
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Incorrect answers are treated is correct.

Looking at the JavaScript code, I found that any value that is a key in the array "regions" is treated as correct for all puzzles.
Lars Nordenström
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My visual abilities fail me - managed to solve the puzzles but cannot see what the picture shows
Gantonian
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@nochum: It can't, so the answer to that one probably isn't 88.
Matthew
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how can a dodecagon with an area of 88 fit inside anything with an area of 62.83~?
nochum
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 2022-12-04 
In November, I spent some time (with help from TD) designing this year's Chalkdust puzzle Christmas card.
The card looks boring at first glance, but contains 11 puzzles. By colouring in the answers to the puzzles on the front of the card in black (each answer appears twice), then colouring remaining squares containing 0s red, and regions containing a star brown, you will reveal a Christmas themed picture.
If you want to try the card yourself, you can download this printable A4 pdf. Alternatively, you can find the puzzles below and type the answers in the boxes. The answers will automatically be found and coloured in black, and appropriate squares and regions will be coloured red and brown...
4 5 6 2 8 2 3 6 7 2 4 2 7 0 9 8 4 4 8 9 7 2 4 7 2 9 7 6 7 3 8 9 6 2 3 9 6 3 0 2 2 6 2 8 8 4 2 2 9 0 4 4 8 2 9 9 7 4 8 7 9 7 3 3 2 6 9 3 0 8 3 8 9 9 6 9 3 0 7 9 6 9 3 2 2 6 7 6 9 6 8 0 9 9 2 6 8 2 8 8 8 7 9 3 7 6 2 9 3 7 5 3 9 1 8 3 2 8 2 2 6 2 2 7 2 8 7 6 7 9 8 8 1 9 9 3 2 7 3 9 3 6 9 2 8 6 9 7 4 2 6 2 6 3 8 9 9 6 0 0 9 3 8 9 3 6 8 3 7 9 0 0 6 8 8 9 8
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@Nicki: If you're correct the picture should look suitably Christmassy
Matthew
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Where can I find out if I am correct?
Nicki
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@Graeme Johnston: If you're right the picture should look suitably Christmassy
Matthew
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Great fun thanks. At first they seem impossible but then a way through appears! How do I get the answers / check if I’m right?
Graeme Johnston
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@Mike: The final picture doesn't have to be symmetric
Matthew
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 2021-12-04 
In November, I spent some time designing this year's Chalkdust puzzle Christmas card.
The card looks boring at first glance, but contains 14 puzzles. By writing the answers to the puzzles in the triangles on the front of the card, then colouring triangles containing 1s, 2s, 5s or 6s in the right colour, you will reveal a Christmas themed picture.
If you want to try the card yourself, you can download this printable A4 pdf. Alternatively, you can find the puzzles below and type the answers in the boxes. The answers will automatically be written in the triangles, and the triangles will be coloured...
14 7 1 8 2 5 6 3 10 4 13 12 11 9 9 8 7 0 3 4 0 8 7
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@HJ: the smallest one does have 6, and Q4 is correct too. I bought the cards and had good fun solving it myself. I’m glad to find this here though to check my answers as when I did the shading it looked like the picture wasn’t quite right. Thanks for the cards Matthew, I look forward to next year’s - no pressure!
Alec
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The only one I'm stuck on is #6. I thought I was doing it right but I'm getting a non-integer answer. I'm assuming the heptagon in question is aligned so one of its sides sits on the diameter of the semicircle, and the opposite vertex sits on the curved edge of the semicircle. Is this wrong?
Seth C
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The version of the card on this page doesn't check if your answers are correct, so it will colour in any number you enter as long as it has the right number of digits.
Matthew
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Wonky solution for #9? On a blank start page, answering "16" gives you red and white puzzle completions, yet we _know_ that 16 is an incorrect answer. Strange?
Attika
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@Matthew: Thanks, I figured they did but it was good to get confirmation.
Dan
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@Dan: one digit numbers count
Matthew
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 2020-12-03 
In November, I spent some time designing this year's Chalkdust puzzle Christmas card.
The card looks boring at first glance, but contains 9 puzzles. By splitting the answers into two digit numbers, then colouring the regions labelled with each number (eg if an answer to a question in the red section is 201304, colour the regions labelled 20, 13 and 4 red), you will reveal a Christmas themed picture.
If you want to try the card yourself, you can download this pdf. Alternatively, you can find the puzzles below and type the answers in the boxes. The answers will be automatically be split into two digit numbers, and the regions will be coloured...
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57
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@JDev: lots of the card will still be brown once you're done, but you should see a nice picture. Perhaps one of your answers is wrong, making a mess of the picture?
Matthew
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I finished all of the puzzles but the picture is far from colored in. Am I missing something?

These puzzles have been a blast!
JDev
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Thanks a lot, Matthew. It was great fun!
Gert-Jan
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@Tara: I initially made the same mistake. Maybe you didn't take into account that 6 is not one of the available digits in question 1?
Sean
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@Tara: Yes, looks like you may have got an incorrect answer for one of the black puzzles
Matthew
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 2019-12-08 
Just like last year, the year before and the year before, TD and I spent some time in November this year designing a Chalkdust puzzle Christmas card.
The card looks boring at first glance, but contains 9 puzzles. By splitting the answers into two digit numbers, then drawing lines labelled with each number (eg if an answer is 201304, draw the lines labelled 20, 13 and 4), you will reveal a Christmas themed picture. Colouring the regions of the card containing circles red, the regions containing squares green, and the regions containing stars white or yellow will make this picture even nicer.
If you want to try the card yourself, you can download this pdf. Alternatively, you can find the puzzles below and type the answers in the boxes. The answers will be automatically be split into two digit numbers, the lines will be drawn, and the regions will be coloured...
×3      ×3      ×3      ×3      ×3
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Rishabh, what do you see that I do not?
Rob Glencairn
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Thanks for the feedback. (I now understand the need for redaction). My son sent me your link as a Xmas present. I must think of an appropriate retaliation. (What is a PDF?)Think I've fixed 1,6 and 9....8 eludes me, for the moment.
Rob
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@Rob: It looks to me like you've made mistakes in questions 1, 6, 8, and 9. The hints from the back of the pdf might help:

1. How many numbers between 1 and 10,000 have 1 as their final digit? How many have 1 as their penultimate digit?

6. How many ways can you write 1? 2? 3? 4? 5? What's the pattern?

8. How many zeros does 10! end in? How many zeros does 20! end in? How many zeros does 30! end in?

9. Carol’s sum is odd. What does this tell you about the 5- and 6-digit numbers?
Matthew
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I'm 71, with one good eye left. What am I missing?
1. 400001
2. 1849
3. 2002
4. 130405
5. 120306
6. 53?
7. 171175
8. 59?
9. 313525
Rob
×2   ×2   ×2   ×2   ×1     Reply
It was fun.
Rishabh
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