After completing the UKMT Maths challenge, you receive a certificate of completion and a key fob.

The key fob always contains a puzzle on it. See this site for previous years. This year it was a cipher:

IMOK 2017


2 50 17. 
0339 03 28 

There is also the hint:

'It may help to think about some of the obvious letters. For example, there are not many choices for “2‘.'

Can anyone decode this?

  • $\begingroup$ What are we looking for? $\endgroup$ – Gintas K Jun 8 '17 at 15:18
  • 5
    $\begingroup$ Hello, welcome to Puzzling. Please see Code Puzzles: What (Not) To Do. Thanks! $\endgroup$ – user58 Jun 8 '17 at 15:20
  • $\begingroup$ what cipher is it using? $\endgroup$ – JMP Jun 8 '17 at 15:23
  • 3
    $\begingroup$ This is from the UKMT 2017 key fob. I have one myself (I recommend you include an image, or I can in a bit) $\endgroup$ – Beastly Gerbil Jun 8 '17 at 16:17
  • $\begingroup$ I have edited this puzzle to expand, and to give more information $\endgroup$ – Beastly Gerbil Jun 8 '17 at 18:36

The code appears to follow a substitution cipher, where each numeric digit corresponds to a letter. Four of them are immediately easy to find.

The first line tells us that: 2=I, 0=M, 1=O, 7=K

Replace them in the message, and then solve for the remaining six digits. In this example you can solve the lines in order.

1. I 5M OK. looks like "I AM OK." So 5=A.
2. M339 M3 I8 looks like "MEET ME IN". So 3=E, 8=N, 9=T.
3. TIM46KT6 can't be much other than "TIMBUKTU". So 4=B and 6=U.

The message becomes:


  • $\begingroup$ Ah thats what I says. I've been pondering this a while now $\endgroup$ – Beastly Gerbil Jun 8 '17 at 17:38
  • $\begingroup$ But what does it mean?! $\endgroup$ – Forklift Jun 8 '17 at 17:43
  • $\begingroup$ @Forklift That you need to book a flight to Timbuktu soon... ;c) $\endgroup$ – BmyGuest Jun 8 '17 at 18:20

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