Number, letter and alphanumeric. The most reliably repeated topic in the whole reasoning section — eight of the questions in this chapter came straight out of the 2021 and 2025 papers.
Every series question in every AAI paper is solved by one habit: write the differences underneath, and treat each position as its own separate series.
Write the gaps between consecutive terms in a row underneath. If those gaps are constant, you are done. If not, write the gaps between the gaps. Almost every AAI number series resolves at this second level.
Row 2 doubles each time, so the next second difference is 40, the next first difference is 55 + 40 = 95, and the answer is 235 + 95 = 330.
Do not look for a clever pattern before you have written both difference rows. Nine times out of ten the pattern is sitting in row two and needed no cleverness at all.
Given OA, LG, IM, FS, ? the instinct is to read each pair as a unit. Do the opposite. Stack the terms vertically and treat the first letters as one series and the second letters as another. They almost never share a rule.
Column one falls by 3 each time, column two rises by 6 each time. Neither knows the other exists — and that independence is the whole technique.
Never read a letter series left to right as words. Write the terms one under the other and work down each column. It converts a puzzle into two easy arithmetic sequences.
XY, RT, LO, FJ, ?
A letter attached to a number, like F5, J8, R14, D23. The letter half and the number half follow completely separate rules, and the number half is often not a simple difference at all — it can be primes, squares or a doubling gap.
Both halves grow, but at different rates. Solve one, then the other, then combine. Never assume the number tells you anything about the letter.
Physically separate the letters from the numbers on your rough sheet before you compute anything. Mixing them on one line is how the two rules get confused.
F5, J8, R14, D23, ?
This is the 2025 signature format: BTE9 DQI12 FNM15 HKQ18 ? Four independent series in one question — three letter columns and one number column. It looks heavy and is actually the most mechanical question on the paper.
Column one rises by 2, column two falls by 3, column three rises by 4, and the number rises by 3. Write all four rules down before you look at a single option.
Draw an actual four-column grid on your rough sheet. The extra five seconds of setup makes all four rules visible at once, and you will never mix up column two with column three again.
When a letter column runs past Z going forwards, or past A going backwards, you wrap. Getting the wrap off by one is the single most common way candidates lose a series mark, and the wrong options are designed around exactly that error.
The one that catches people is landing on zero. Position 0 is not A — it is Z, because 0 + 26 = 26. In the 2021 Shift 2 question, column one lands on exactly 0, and option 3 exists purely for candidates who answer A.
Say it once before every series question. It is worth roughly one mark per paper on its own.
Four pages of practice covering all four series types, with a printable alphabet-position strip and ruled grid space for your column working. Print it, solve it, keep it.
Multiple choice and assertion–reason, building in difficulty. Full solutions are in the downloadable PDF above.
Live classes cover every reasoning, aptitude, English and GK topic straight from the real papers, with the shortcut for each question type drilled until it is automatic.