Letter Codes & Sequences

Letter codes and sequences

These verbal reasoning questions use the alphabet as a puzzle. The key skill is knowing each letter's position number and spotting how letters change.

The alphabet positions

Learn these — they're the foundation of every code question:

A B C D E F G H I J K L M
1 2 3 4 5 6 7 8 9 10 11 12 13
N O P Q R S T U V W X Y Z
14 15 16 17 18 19 20 21 22 23 24 25 26

A useful checkpoint: M = 13 (middle), so N onwards is the second half.

Letter sequences

Work out how the letters jump each step.

• AB, CD, EF, ? → each pair moves on by 2 letters → next is GH.
• A, C, E, G, ? → +2 each time → I.
• Watch for two patterns: e.g. the first letter goes forward while the second goes backward.

Letter codes

A word is turned into a code by shifting each letter forward or backward by a set number.

• Example: if CAT is coded as DBU, each letter moved +1 (C→D, A→B, T→U). To code DOG the same way: EPH.
• To crack a code, compare the word and its code letter by letter to find the shift.

Number–letter codes

Sometimes letters are given number codes based on their position (A = 1, B = 2…). Work out the word's positions, apply any rule, then convert back.

Wrapping around

If a shift goes past Z, it wraps back to A (Z + 1 = A). Likewise A − 1 = Z. Keep this in mind for shifts near the ends of the alphabet.

Worked example

If DOG is coded FQI, what is the code for CAT?

• D→F (+2), O→Q (+2), G→I (+2): the shift is +2.
• CAT: C→E, A→C, T→V → ECV. ✓

Common mistakes

• Getting the alphabet positions wrong (miscounting).
• Forgetting to wrap around from Z back to A.
• Applying the shift in the wrong direction (forward vs backward).

Top tips

• Memorise the alphabet with numbers, using M = 13 as a checkpoint.
• Find the shift by comparing one letter and its code.
• Write the alphabet at the top of your paper to count quickly.

Quick recap

• Know alphabet positions (A = 1 … Z = 26; M = 13).
• Sequences: find how letters jump each step (sometimes two patterns).
• Codes: find the shift by comparing letters; remember to wrap Z → A.