Letter Series Patterns and Solved Questions
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Key points
- Convert letters to numbers before looking for the pattern
- Reusing the previous gap instead of continuing the pattern is the commonest trap
- In pair series the first letters and second letters follow separate rules
- A pair that seems to move backwards means wrap-around past Z
- In group series check the gap inside the group and between groups
- In missing-letter questions find the repeating block first
On this page
Constant gap
Example
Z, W, T, Q, N, ? The positions are 26, 23, 20, 17, 14, falling by 3 each time, so the answer is 14 − 3 = 11, which is K.
Increasing gap
Example
A, C, F, J, O, ? The positions are 1, 3, 6, 10, 15 and the gaps are 2, 3, 4, 5. The next gap is 6, so the answer is 15 + 6 = 21, which is U. Reusing the gap of 5 gives T, the trap option.
Opposite-letter pairs
Example
AZ, BY, CX, DW, ? The first letters move forward and the second letters backward, each pair adding to 27. After D comes E, whose opposite is 27 − 5 = 22, which is V. So the answer is EV.
Alternate series
Example
B, Y, D, W, F, U, H, ? Odd positions run B, D, F, H rising by 2. Even positions run Y, W, U falling by 2. The blank is the eighth term, an even position, so the answer is 21 − 2 = 19, which is S.
Letter groups
Group questions carry two rules at once: one inside each group and one between groups.
Example
ACE, BDF, CEG, ? Inside each group the gap is +2. Between groups each letter moves +1. So the next group starts at D and runs D, F, H, giving DFH.
Two rules with wrap-around
Example
KM, NQ, RV, WB, ? The first letters move +3, +4, +5, so the next is +6: W at 23 plus 6 = 29, and 29 − 26 = 3, which is C. The gap inside each pair runs +2, +3, +4, +5, so the next is +6: C at 3 plus 6 = 9, which is I. The answer is CI. Note that W to B in the fourth pair is itself a wrap-around, since 23 + 5 = 28 and 28 − 26 = 2.
Missing-letter series
These questions give a repeating string with blanks. Find the repeating block first, then fill every blank so that all blocks read alike.
Example
a _ b b a _ b b a a _ b. Split into blocks of four: a _ b b, a _ b b, a a _ b. Each block must read a a b b, so the blanks are a, a and b, and the completed string is aabb aabb aabb.
Odd one out
Example
Among BDF, RTW, MOQ and GIK, three groups use a gap of +2 twice. RTW runs 18, 20, 23 with gaps +2 and +3, so it is the odd one. The matching group would have been RTV.
Exam tip
Write the position numbers under the letters before doing anything else. These questions are fully solvable, so there is no need to guess, but they are easy to get wrong by counting in the head.
Practice questions
Answer all, then check. Explanations appear after checking.
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