How to solve letter series questions
Letter series are number series in disguise
Convert letters to positions, and every letter series becomes an easy number series — with one extra rule: the alphabet wraps.
Updated
C, F, I, L, ? terrifies exactly until you write 3, 6, 9, 12 — then it's a school exercise. Letter series test whether you know to translate. Learn the anchor positions and the translation is instant.
Anchors and translation
Memorize anchors: A=1, E=5, J=10, M=13, N=14, T=20, Z=26. Every other position is one hop from an anchor. Translate the series, run the number-series ladder (differences first!), translate back.
The wrap
After Z the series re-enters at A: X +3 → A. A 'broken' pattern near the end of the alphabet almost always wrapped. Treat positions modulo 26 and the break disappears.
Interleaving strikes here too
Two braided letter series (positions 1,3,5 vs 2,4,6) explain most hard items. If the raw differences look chaotic, split odd/even positions before trying anything clever.
The strategy
- Translate to numbers immediately — never reason in letters.
- Differences first, growing steps second, alternation third, interleaving fourth.
- Wrap with mod 26 when steps cross Z.
- Translate your predicted position back and match the options.
Common traps
- Off-by-one translation (K is 11, not 10).
- Missing the wrap and abandoning a correct rule.
- Answering with the letter one step early — re-count before committing.
Speed · ~30s/item: Translation costs 10 seconds and saves 40. Total budget 20–45 seconds.
Try it yourself: 1 practice questions
Pick an answer, then reveal it. Nothing is recorded, there is no clock, and none of these questions is ever used in a test.
What comes next in the series?
Reveal the answer
The answer is E — F.
Show why — the worked reasoning
Try questions like this
The free test has 20 questions across abstract, numerical, verbal and spatial reasoning. It takes 12 minutes, needs no sign-up, and explains every answer.
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Questions people ask
Will letter series questions be on the free test?
Maybe. The free test gives verbal & logic 5 of its 20 questions, spread across 11 different question types, so any one test may or may not include this kind.