Series (Number & Letter)
🔒 Log in to trackLetter series
🔒 Log in to trackLetters hide number series. Convert A=1 ... Z=26 (EJOTY: E=5, J=10, O=15, T=20, Y=25) and every letter series becomes a number series with wrap-around after Z.
Typical CGL letter rules:
- Constant step per letter: B, D, F, H (+2 each).
- Rising step: B, D, G, K, P (steps 2, 3, 4, 5).
- Alternating steps: A, C, B, D, C, E (steps +2, −1 repeating).
- Two-track clusters: in 'AZ, BY, CX' the first letters climb +1 while second letters fall −1.
Treat multi-letter clusters slot by slot — each letter-position is its own mini-series.
Detailed notes
Letters are numbers in disguise
Every letter series is a number series written in letters. Give each letter its place in the alphabet: A=1, B=2 ... Z=26. Now 'C, G, K, O' is just 3, 7, 11, 15 — add 4 each time. The next is 19 = S.
Learn the anchors: EJOTY
Counting from A every time is slow and causes mistakes. Remember five anchor letters:
| E | J | O | T | Y |
|---|---|---|---|---|
| 5 | 10 | 15 | 20 | 25 |
Any letter is one or two steps from an anchor: M = O − 2 = 13, R = T − 2 = 18, W = Y − 2 = 23.
Also learn the reverse position (Z=1, Y=2 ... A=26). Rule: reverse position = 27 − position. The opposite pairs add up to 27: A-Z, B-Y, C-X, D-W, E-V, F-U, G-T, H-S, I-R, J-Q, K-P, L-O, M-N.
Wrap-around
After Z the alphabet starts again at A. If a rule gives a number above 26, subtract 26: X(24) + 4 = 28 → 28 − 26 = 2 = B. Going backwards below A, add 26: C(3) − 5 = −2 → −2 + 26 = 24 = X.
Type 1: constant step
Every letter moves by the same number: C, G, K, O, S (+4). It can go backwards too: Z, W, T, Q (−3). It can cross Z: T, W, Z, C, F (+3).
Type 2: rising or falling step
The step itself changes: C, D, F, I, M (+1, +2, +3, +4, so next +5 → R). Or Y, W, T, P, K (−2, −3, −4, −5, so next −6 → E).
Type 3: two series mixed
Positions 1, 3, 5 form one series and positions 2, 4, 6 another: A, Z, C, X, E, V → A, C, E (+2) and Z, X, V (−2). Or the steps take turns: B, E, D, G, F, I (+3, −1, +3, −1).
Type 4: letter clusters
Each term is a group of 2-4 letters: BDF, GIK, LNP. Treat each position as its own series: first letters B, G, L (+5), second letters D, I, N (+5), third letters F, K, P (+5). Next: QSU. The slots can move in different directions: AZ, CX, EV (first letter +2, second letter −2).
Type 5: positions follow a number pattern
The positions themselves may be squares (A, D, I, P, Y = 1, 4, 9, 16, 25) or primes (B, C, E, G, K = 2, 3, 5, 7, 11).
Method in four steps
- Write the position number under every letter (use EJOTY).
- Find the number rule with the difference ladder.
- Apply it, using wrap-around if the result passes 26 or goes below 1.
- Convert back to a letter and match the option.
Quick revision
- A=1 ... Z=26; anchors E5, J10, O15, T20, Y25.
- Reverse position = 27 − position; opposite pairs add to 27.
- Above 26 → subtract 26; below 1 → add 26.
- Clusters: solve each slot separately.
- Letters going forward and back → split into two series.
- Squares (A, D, I, P, Y) and primes (B, C, E, G, K) are favourite hidden rules.
Types of questions asked
Every way this subtopic shows up in exams — how to recognise it, the formula or logic to use, and a solved example.
Type 1: Single letters with a constant step (forward, backward, wrap-around)very common3 practice Q
Single letters that move the same distance each time, e.g. D, H, L, P.
- Convert letters to positions (EJOTY anchors).
- Find the constant step.
- Add it; if the result passes 26, subtract 26 (below 1, add 26).
Why it works: a letter series is a number series in disguise.
Example: D, H, L, P, ?
Positions 4, 8, 12, 16 → +4. 16 + 4 = 20 = T.
Type 2: Rising or falling step between lettersvery common3 practice Q
The gaps between letters grow (+1, +2, +3) or shrink by a fixed amount.
- Write positions and the step row.
- Continue the step row.
- Add the next step to the last letter.
Why it works: it is the letter version of the growing-difference number series.
Example: A, C, F, J, O, ?
Steps +2, +3, +4, +5 → next +6. O(15) + 6 = 21 = U.
Type 3: Two letter series mixed (alternate letters or alternating steps)common2 practice Q
Letters jump forward and back, or the same two steps keep taking turns.
- Split odd places and even places, or write the step row.
- Solve each small series, or continue the step cycle.
- Pick the series that the '?' belongs to.
Why it works: two simple rules written one after the other look messy only when read together.
Example: B, Y, D, W, F, U, ?
Odd places B, D, F (+2) → next H. Even places Y, W, U (−2). The 7th term is an odd place → H.
Type 4: Letter-cluster series (each slot is its own series)very common3 practice Q
Every term is a group of 2-4 letters, e.g. AC, EG, IK.
- Take the first letter of every cluster — find its rule.
- Do the same for the second letter, third letter ...
- Join the next letters of all slots.
Why it works: each slot moves by its own rule, often the same step, sometimes opposite directions.
Example: AC, EG, IK, ?
First letters A, E, I (+4) → M. Second letters C, G, K (+4) → O. Answer MO.
Type 5: Letter positions follow squares or primesoccasional2 practice Q
The steps look irregular, but the positions are 1, 4, 9, 16 ... or 2, 3, 5, 7, 11 ...
- Write the positions of all letters.
- Check squares and primes directly on the positions.
- Take the next square or prime and convert it to a letter.
Why it works: the examiner hides a famous number list behind letters.
Example: C, E, G, K, M, ?
Positions 3, 5, 7, 11, 13 are primes. Next prime 17 = Q.
Formulas
Steps per slot decide the rule; wrap Y→B counts as +3.
Tracks are independent; solve both.
Shortcut tricks
⚡ Step row under the letters
Write positions over the letters and steps between them. One clean step row (+2, +2, +2...) or a rising row (2, 3, 4, 5) ends the question.
Example: Q. B, D, G, K, ?
Sol. Steps: +2, +3, +4 → next +5. K(11) + 5 = P(16) → P.
Steps convert letters to arithmetic — never eyeball letter gaps.
⚡ Wrap-around fluency
After Z the alphabet restarts: Y + 4 = C. Practise from EJOTY anchors — every jump is at most 13, take the shorter direction.
Example: Q. X, Z, B, ?
Sol. X(24) +2 = Z(26), Z + 2 = B(2), B + 2 = D. The +2 step survives the wrap.
Wrap steps are the number one source of wrong letter answers — always add positions mod 26.
Where students lose marks
Counting backwards through Z incorrectly (Z − 2 is X, not 'nothing').
Missing rising steps: treating +2, +3, +4 as a flat '+3 average' gives a wrong letter.
Applying one track's step to both tracks of a cluster pair.
Practice sets — 17 questions
Sets of 10, mixed across the question types above. Each answer comes with a step-by-step explanation.
Topic test · 10 questions
Suggested time 5 min · wrong answers go to your mistake notebook automatically.