The number and letter series test widens the classic sequence puzzle into seven pattern families and then hides the gap anywhere it likes, sometimes in the middle of the row. Numbers, letters, and hybrid items like B3 and D6 all follow rules, and thirty questions ramp through them with a shrinking clock. This guide maps the families, the diagnosis order that identifies them fast, and the letter arithmetic most candidates never bother to learn.
What is the Number and Letter Series Test?
The test measures inductive reasoning across notations: the rule extraction skill of a classic series test, stretched over numeric, alphabetic and mixed alphabets. The letter strand is the differentiator. Treating the alphabet as a number line, where C plus two is E and the strides can grow, turns letter questions into arithmetic; candidates who never make that conversion solve them by recitation and lose the clock.
The seven families: arithmetic steps, geometric ratios, polynomial sequences built on squares, cubes and triangular numbers, alternating double rules, letter series with fixed strides, letter series with growing strides, and mixed alphanumeric pairs where both halves advance by their own rule. The pilot battery's number series test covers the numeric core; this ATC version adds the letters and the hybrids on top.
Which Exams Include the Number and Letter Series Test?
Series items spanning numbers and letters are widespread in selection. Candidates commonly report this test type in:
- FEAST and related ATC selection batteries, in reasoning stages
- DLR screenings, where series items extend into letter forms
- COMPASS and Advanced COMPASS by EPST, in reasoning sections
- ADAPT, within its cognitive battery
- Aon / cut-e batteries, in inductive reasoning scales
Providers change their content without notice and publish no official syllabus, so treat this as candidate-reported guidance.
How the Test Works: Format and Rules
The frame:
- 30 questions with an automatic difficulty ramp; four options each.
- The gap can sit mid-sequence, not only at the end, so the rule must explain both directions from the hole.
- Number families: constant steps, ratios, polynomials, alternating rules.
- Letter families: fixed strides like B, D, F, H and growing strides like A, B, D, G.
- Hybrids like B3, D6, F9 advance letter and number by separate rules simultaneously.
Take 3, 6, 12, ?, 48. The ratios read times two, times two: a geometric series. Twelve doubled is 24, and 24 doubled confirms at 48. This is exactly how it looks in the test:
The options and the clock complete the picture:
One glance decides the family: differences for numbers, strides for letters, and both at once for the hybrids.
Scoring: What a Good Result Looks Like
Accuracy with response time across the ramp. The distractors continue rival rules, the value that fits an additive reading of a geometric series being the classic. Strong candidates confirm the rule on both sides of a mid-sequence gap before answering and keep pace as the families harden; the letter and hybrid questions late in the set are where prepared candidates separate from fluent guessers.
How to Prepare: Strategies That Actually Work
- Run the same diagnosis order every time. Differences first; if they are constant, done. If they grow, check ratios and polynomials. If they alternate wildly, split the strands.
- Learn letter positions cold. A1, E5, J10, O15, T20, Z26 as anchors, and the rest by counting from them. Letter arithmetic at speed depends on this table.
- Translate letters to numbers on paper-free reflex. B, D, G, K reads as 2, 4, 7, 11, and the growing stride plus two, plus three, plus four appears instantly.
- Split hybrids into two series. B3, D6, F9: letters stride by two, numbers by three. Solve each strand alone; never juggle them fused.
- Use mid-gaps as double checks. A hole in the middle gives you rule evidence on both sides; the correct answer must satisfy both, which kills most distractors.
- Keep the numeric core sharp. The number series test drills the difference-taking engine this test runs on.
Common Mistakes to Avoid
- Reciting the alphabet from A for every letter question instead of using anchors.
- Extending only the left side of a mid-sequence gap.
- Fusing hybrid items into one impossible rule instead of splitting strands.
- Committing to the first family that fits two terms; polynomials imitate arithmetic for exactly that long.
Practice This Skill
Family recognition compounds with exposure, and the letter strand rewards a single week of anchor drilling. Train with the Number and Letter Series module, which reproduces the seven families, the mid-sequence gaps and the 30 question ramp exactly as described here. Level 1 is free, and the guided tutorial walks you through the format before your first attempt.