SSC CHSL · Bite-size lessons

Series

About 6 min · General Intelligence and Reasoning · English

Time worked out from the lesson's 399 words at 150 words a minute, plus a minute for each question.

Series problems test your ability to identify patterns and predict the next term in a sequence. The question presents a sequence of numbers, letters, or mixed elements with one term missing (usually at the end), and you must spot the underlying rule to find it.

Key ideas

• Number Series: Sequences of numbers following arithmetic (+/– constant), geometric (×/÷ constant), or mixed operations. Common sub-types include difference series (differences themselves form a pattern), square/cube series (terms are perfect powers), prime number series, and alternating patterns (odd/even positions follow different rules).
• Alphabet Series: Letters arranged by position values (A=1, B=2…Z=26). Patterns include adding/subtracting constant positions, skipping letters in fixed intervals, and reverse alphabets (Z=1, Y=2…A=26). Remember EJOTY—the five letters at positions 5, 10, 15, 20, 25 are useful landmarks.
• Alphanumeric Series: Mixed sequences of letters and numbers. Typically the numeric part and alphabetic part follow independent patterns. Solve by separating them into two sub-series, finding each pattern individually, then recombining.
• Alternating Series: Odd-positioned terms follow one rule, even-positioned terms follow another. Always check if splitting into two interleaved sequences reveals simpler patterns.
• Difference Method: Write the differences between consecutive terms. If those differences form a recognizable pattern (constant, arithmetic, geometric), you've found the rule. For stubborn series, try second-level differences (differences of differences).

Watch out for

• Ignoring alternating patterns → Always check odd/even positions separately when direct differences fail. A flat or erratic difference sequence often signals two interleaved patterns.
• Forgetting reverse alphabet values → If letter positions seem random or decreasing oddly, recalculate using Z=1, Y=2…A=26.
• Stopping at first-level differences → If differences don't show clear pattern, compute second-level differences (differences of differences). Some series hide patterns two layers deep.

Quick reference

• Split alternating series into odd/even positions—solve two simpler series instead of one complex one.
• Memorize squares 1–20, cubes 1–10, primes up to 71, and EJOTY positions (5, 10, 15, 20, 25).
• For alphabet series, convert letters to numbers immediately (A=1…Z=26) then apply arithmetic.
• Use the difference method: write term differences, then differences of differences if needed.
• In alphanumeric series, separate letters and numbers into independent sub-series before solving.

Check yourself: 3 questions

This lesson is cut from the topic's note, not rewritten. Fact-checked on 18 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.

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