Long strings of letters, numbers and symbols with a "how many are preceded by… and followed by…" question attached. Two or three marks in every 2025 shift, and pure procedure once you stop reading and start scanning.
There is no cleverness in this chapter at all. There is a procedure, and candidates who follow it score; candidates who eyeball the string do not.
Every one of these questions describes a window of three consecutive elements: something before, the thing you are counting, and something after. Write that window down before you read the string.
Now you are not solving a puzzle, you are matching a three-character pattern across a string. Slide the window one place at a time and tick every match.
Counting always runs left to right only — every AAI question states this explicitly. The first element can never qualify if the condition needs something before it, and the last element can never qualify if the condition needs something after it. Those two exclusions alone remove the most common wrong answer.
Write the three-slot pattern in the margin before your eyes go anywhere near the sequence. Reading the string first and the condition second is how people end up counting the wrong thing.
The string is pure letters and the condition is built on vowels and consonants. Mark every vowel before you start scanning; the consonants are then everything you did not mark.
Underline or circle each vowel in one quick pass. The scan afterwards becomes a matter of looking at marks rather than reading letters, which is roughly twice as fast.
How many consonants are there in the following series, each of which is immediately preceded by a vowel and also immediately followed by a vowel?
Once the vowels are circled, you are looking for two circles with exactly one letter between them. Nothing else on the page matters.
The string is single digits and the condition uses odd, even, prime or perfect square. AAI adds a bracketed note when a definition might be disputed — in 2025 it printed "1 is a perfect square" so nobody could argue.
Note that 0 is usually absent from these strings, and that 1 counts as a perfect square but not as a prime. Both of those are examiner favourites.
How many perfect squares are there, each of which is immediately preceded by an even digit and immediately followed by an odd digit? The paper notes that 1 is a perfect square.
In a single-digit string there are only three perfect squares, so start by circling every 1, 4 and 9. There are usually six or seven of them, and each takes two seconds to test.
Both 2025 shifts carried a symbol question, and both used the identical condition: symbols preceded by something and followed by another symbol. The trick is that consecutive symbols disqualify each other on the left.
If the condition needs a letter or a number immediately before, then inside a run of three symbols only the first one has a non-symbol before it. The second and third are automatically out. That observation kills most candidates in one line.
How many such symbols are there, each of which is immediately preceded by a letter and also immediately followed by another symbol?
Do not scan symbol by symbol. Scan for places where two symbols sit side by side, because the condition demands one. Then check what comes before each run. In a 29-element string this reduces the work to two or three checks.
These questions are not difficult, so the examiner builds the difficulty into the wording. Five traps account for almost every wrong answer.
Before anything else, circle the word "and" in the question if it is there. It is the single word that decides whether you check one neighbour or two.
Practice covering letter, number and symbol sequences, with every string printed in wide monospace so you can mark it up directly on the page. 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.