Question Type 3: Letter Codes

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With this question type, we enter the realm of logic. Vocabulary now becomes less important, and instead we need to use a process that is more similar to Maths than it is to English.

What does this question type involve?

Here, you will be presented with a copy of the alphabet to help you as you solve the puzzle. You will be given a code for a particular word, and then asked either what another set of letters would mean, or what letters you would need to use to code a different word.

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Example questions

If the code for BANK is CBOL, what does SBOL mean?

Answer: RANK

Here’s a simple one to begin. The code is +1 for each letter – i.e. A is written as B, B is written as C, etc.

If the code for BANK is CCQO, what does QQPT mean?

Answer: POMP

Here’s a slightly more complex one. The code is +1, then +2, then +3, then +4 for each letter in turn. As such, we need to translate QQPT using this same technique. Q therefore becomes P, the letter before. The second Q must be two letters before, so it is an O. The third P becomes M, three letters before, and the T becomes a P, four letters back. Therefore the word is POMP.

The CASM Approach to Type 3

The CASM approach means that you should check whether the code is:

Your first step is to look at whether the code is constant. Can you form the word by simply going +1,+1 across the whole word? What about using +2,+2 etc across the whole word? This is the most basic code type and you should see if it works through 1,2,3 or even 1,2,3,4 quickly.

If this doesn’t work, then you must move on to an additional code. Here, you should either add one more each time moving across, or try subtracting one each time. The code might be +1, +2, +3 etc, or it could be +2,+4,+6 etc. Alternatively, it might involve something like 0,-1,-2,-3 etc, or -2,-4-6,-8 etc. Make sure to check both of these options before moving onto the next stage.

Changing the signs alternately can make the code a lot more difficult. This could involve a +1, -1, +1 code, for example. Taking it to a more difficult level, it could even involve something like +1,-2,+3,-4. To spot this you will likely need to be aware of this code type and check it.

If you still haven’t cracked the code, then try a mirror instead. The final common pattern is that all letters are mirrored around a point in the alphabet (typically the centre of the alphabet). 

Worked Example

Let’s imagine that you are presented with the code TJDI and told that it means SLAM. What could the code be?

We start with constant codes. Adding 1 across each time doesn’t work, nor adding two. In fact, it’s clear that there’s more going on than that. The letters aren’t moving just back, or just forward. So, we try an additional code. Perhaps they are adding one more each time, or subtracting one more? Once again, no luck. Next, we need to try flipping the signs, and using a constant code. Again, no luck. Next, we try a code where we both change the signs and add one more each time. We find that +1, -2, +3, -4 works.

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Top Tricks

You simply have to work through the process here, and trust that it will help you to find the answer. Practising a lot, and getting used to spotting patterns using the process above, will set you in good stead. 

Common Pitfalls

Failure in these questions could come from forgetting one of the different codes above, or one of the variations. If you remember them, you will be fine!


In summary, these questions can range greatly in difficulty, and it is highly likely that there will be at least one question that you struggle with. Remember to move on if a question takes too long – but only after you’ve exhausted the CASM process.
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