Series in Aptitude – Complete Guide
In aptitude tests, a series is a sequence of numbers, letters, or symbols arranged in a logical order based on a hidden rule. Your task is to find the rule and predict the next, missing, or wrong term.
1. Main Categories of Series
A. Number Series
A chain of numbers arranged according to a mathematical logic.
Common Patterns:- Direct Addition / Subtraction – Example: 7, 10, 13, 16, 19, … (+3 each step)
- Multiplication / Division – Example: 3, 6, 12, 24, 48, … (×2 each step)
- Multiple Operations – Example: 2, 4, 12, 48, 240, … (×2, ×3, ×4, ×5 …)
- Perfect Squares / Cubes – Example: 1, 8, 27, 64, … (1³, 2³, 3³, 4³)
- Prime Numbers – Example: 2, 3, 5, 7, 11, 13, …
- Fibonacci / Summation Pattern – Example: 1, 1, 2, 3, 5, 8, … (Sum of previous two terms)
B. Alphabet Series
Letters follow a logical jump forward or backward in the English alphabet.
Example: A, D, G, J, … (Each letter is 3 positions ahead)
Tip: Convert letters to numbers (A=1, B=2, … Z=26) to see the pattern faster.
C. Mixed Series
A combination of numbers, letters, or symbols where each part follows its own rule.
Example: A1, C2, E3, G4, … (Letter jumps + Number increases by 1)
2. Step-by-Step Solving Approach
- Find the Difference – Subtract consecutive terms.
- Check Ratios – Divide consecutive terms.
- Spot Alternate Rules – Even and odd positions may have different patterns.
- Look for Special Numbers – Squares, cubes, primes, factorials, Fibonacci sequence.
- Test for Repeating Cycles – See if the same group repeats.
3. Quick Exam Shortcuts
- Slow growth → usually addition/subtraction.
- Fast growth → often multiplication/powers.
- Changing differences → check if differences form their own pattern.
- Symbols/letters with numbers → treat separately.
4. Practice Formula Mindset
- nth term of an AP = a + (n−1)d
- nth term of a GP = a × r^(n−1)
- Fibonacci logic → Tâ‚™ = Tâ‚™₋₁ + Tâ‚™₋₂