Number Series

Medium

Number series problems require identifying the pattern in a sequence of numbers and finding the next (or missing) term.

Why It Matters

One of the highest-frequency question types in placement aptitude and banking exams. Tests pattern recognition speed.

How It Works

Common patterns to check (in order): constant difference (AP), constant ratio (GP), difference of differences (quadratic), alternating operations (+3, ×2, +3, ×2), perfect squares/cubes ± constant, prime number series, Fibonacci-like (each term = sum of two previous), two interleaved series (odd positions follow one pattern, even positions another). Strategy: write the differences between consecutive terms. If those aren't constant, write the second differences.

Example

Series: 2, 6, 18, 54, ? — Each term × 3 → next = 162 (Geometric Progression with ratio 3).

Common Mistakes

Students often try only addition/subtraction patterns and miss multiplicative or alternating patterns. Another trap: seeing a pattern in the first few terms that breaks later.