Letter Sequences & Codes

In this lesson, you will learn how to tackle letter sequence and letter code questions. These involve spotting patterns in letters, often linked to their position in the alphabet. They might look tricky at first, but with practice, they become straightforward.

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The Alphabet — Your Most Important Tool

For these questions, you must know the alphabet and the position of each letter. Here it is with numbers:

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

Top tip: Learn these positions by heart! Knowing that M = 13 (the middle of the alphabet) is particularly useful. You can count forwards from A or backwards from Z.

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Part 1: Letter Sequences

What Is a Letter Sequence Question?

You are given a series of letters and must find the next letter (or the missing letter) in the pattern.

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Worked Example 1: Simple Forward Pattern

Question: What comes next?

A C E G ?

Step-by-step:

1. Write the positions: A=1, C=3, E=5, G=7
2. Find the pattern: 1, 3, 5, 7 — each number increases by 2.
3. Next: 7 + 2 = 9 = I
4. Answer: I

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Worked Example 2: Backward Pattern

Question: What comes next?

Z X V T ?

Step-by-step:

1. Positions: Z=26, X=24, V=22, T=20
2. Pattern: 26, 24, 22, 20 — each decreases by 2.
3. Next: 20 - 2 = 18 = R
4. Answer: R

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Worked Example 3: Increasing Gap

Question: What comes next?

A B D G K ?

Step-by-step:

1. Positions: A=1, B=2, D=4, G=7, K=11
2. Differences: +1, +2, +3, +4
3. The gap increases by 1 each time. Next gap: +5
4. 11 + 5 = 16 = P
5. Answer: P

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Worked Example 4: Alternating Pattern

Question: What comes next?

A Z B Y C ?

Step-by-step:

1. There seem to be two sequences woven together:
   • Odd positions: A, B, C — going forward through the alphabet.
   • Even positions: Z, Y — going backward through the alphabet.
2. The next letter is in an even position, so it continues the backward sequence: Z, Y, X.
3. Answer: X

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Worked Example 5: Letter Pairs

Question: What comes next?

AB CD EF GH ?

Step-by-step:

1. Each pair is two consecutive letters: AB, CD, EF, GH.
2. The pattern moves forward by 2 letters each time.
3. Next pair: IJ
4. Answer: IJ

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Common Letter Sequence Patterns

Pattern Type	Example	Rule
Skip 1 letter	A, C, E, G, I	+2 each time
Skip 2 letters	A, D, G, J, M	+3 each time
Backward skip 1	Z, X, V, T, R	-2 each time
Increasing gap	A, B, D, G, K, P	+1, +2, +3, +4, +5
Decreasing gap	Z, Y, W, T, P	-1, -2, -3, -4
Alternating	A, Z, B, Y, C, X	Forward + backward combined
Double letters	AA, CC, EE, GG	Skip 1, doubled
Reversed pairs	BA, DC, FE, HG	Consecutive pairs, reversed

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Part 2: Letter Codes

What Is a Letter Code Question?