## Coded message brainteaser

By David Shaw, 21 March 2018

You’ve just received a secret coded message:

AD, BA, BH, CE, DB, DI, EF

You know it follows a pattern, but can you work out what pair of letters come next?

Scroll down for the answer!

## Brainteaser answer

You might have noticed that the first letter in each term is further along the alphabet. This could be considered a clue. And what if the pairs of letters represented numbers?

You can convert the letters to numbers using a simple substitution cypher:

A = 1, B = 2, C = 3 and so on.

This gives us the sequence:

14, 21, 28, 35, 42, 49, 56

You might notice that they’re all multiples of seven! That means the next number in the sequence is 63.

Taking it back through the substitution code, we get the answer, FC.

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23 March, 2018 at 2:50 pm

I did it differently but still got it, as the number of letters for the first one goes 1, 2,1,2,1 and goes up A,b,c etc. while the second letter in each increase by one letter. The letters that have one letter so the A,C and E have the second letter D,E,F so goes up one while the two numbers go up in the same order but start at A and H and therefore when you get to the next one in the order it is FC.

23 March, 2018 at 2:55 pm

That’s a clever pattern! It might reveal something special about the seven times table. Have you tried extending the pattern even further? does it still make sense?

24 March, 2018 at 4:01 pm

What a great code challenge for us to do over lunch!

25 March, 2018 at 7:02 pm

I looked into the pattern further and it holds up.

AD 14

BA 21

BH 28

CE 35

DB 42

DI 49

EF 56

FC 63

FJ 70

GG 77

HD 84

HK 91

IH 98

JE 105

JL 112

KI 119

LF 126

LM 133

MJ 140

NG 147

NN 154

OK 161

PH 168

PO 175

QL 182

RI 189

RP 196

I’m not sure as to why it works for all the letters but would be interesting to find out why it does that. Do you have any ideas?

25 June, 2021 at 4:37 pm

I love these brainteasers like wtf