Series Questions for SSC CHSL

Types of Series You Must Know

SSC CHSL series questions fall into three broad families: Number Series (pure digits), Letter Series (alphabets with position logic), and Mixed or Alphanumeric Series (letters plus numbers together). Within each family, the pattern is always one of a handful of templates. Once you identify the template, the answer is mechanical.

• Number Series: arithmetic (add/subtract), geometric (multiply/divide), squares, cubes, prime numbers, two-step alternating patterns.
• Letter Series: based on alphabetical position (A=1, B=2 ... Z=26), gaps between letters follow arithmetic or geometric rules.
• Mixed Series: a number and a letter change together — track them separately then combine.
• Wrong Term Series: one term breaks the pattern — find the odd one out.
• Missing Term Series: a blank is given — fill in the correct value.

The 5 Most Common Number Series Patterns in CHSL

Roughly 80 percent of CHSL number series questions use only five templates. Memorise these five and you can crack most questions without deep calculation. Always check these in order — start with the simplest (add/subtract) and move to more complex (squares, cubes).

• Pattern 1 — Constant Difference: 4, 7, 10, 13... (add 3 each time).
• Pattern 2 — Increasing Difference: differences themselves go up by a fixed number (like 2, 4, 6, 8...).
• Pattern 3 — Squares or Cubes: 1, 4, 9, 16, 25 or 1, 8, 27, 64.
• Pattern 4 — Multiply/Divide: 2, 6, 18, 54 (x3 each step).
• Pattern 5 — Two Interleaved Series: odd positions form one series, even positions form another. Example: 2, 3, 4, 6, 6, 12... (even positions x2, odd positions +2).

Letter Series Strategy

In letter series, always convert each letter to its alphabet number first. Then find the gaps between consecutive numbers. The gap pattern will follow one of the numeric series templates above. After finding the next number, convert back to a letter. EJOTY is your best friend here — a quick reference mnemonic for positions 5, 10, 15, 20, 25.

• EJOTY trick: E=5, J=10, O=15, T=20, Y=25. Use this to jump to any position fast.
• Reverse alphabet also appears: Z=1, Y=2... (CHSL tests this occasionally). A=26 in reverse.
• If gap between letters is constant, it is a simple AP series in alphabet form.
• Watch for wrapping: after Z (26), the series may wrap back to A (1).
• For two-letter or three-letter groups, handle each position separately.

Mixed and Alphanumeric Series

These questions give a series like A2, C4, E8, G16, ? where letters and numbers both change. The trick is to split the series into two independent streams — one for letters, one for numbers — solve each separately, then stitch the answer back. Do not try to see both simultaneously; that wastes time and causes errors.

• Step 1: Write only letters in a row. Find letter pattern.
• Step 2: Write only numbers in a row. Find number pattern.
• Step 3: Combine for final answer.
• Common patterns: letters go in steps of 2, numbers double — or letters go +3, numbers are squares.
• In CHSL, mixed series appear at moderate difficulty — usually 1 or 2 questions per paper.

Wrong Term Series — How to Tackle

In wrong term questions, all terms except one follow the pattern. Your job is to find the term that does not fit. The best approach: check the pattern using the first three or four terms to establish the rule. Then verify each term. The one that breaks the rule is the answer. Do not just look at adjacent pairs — always confirm the rule from the start.

• Establish pattern from first 3 terms confidently before checking the rest.
• Squares and cubes series are favourite hiding spots for wrong terms (e.g., 125 replaced by 124).
• In arithmetic series, calculate all differences and spot the one difference that does not match.
• If pattern involves multiplication, check each ratio. One ratio will be different.
• Double-check your suspect term — examiners love placing the wrong term in position 4 or 5.

• Jumping to answer after checking only two terms — always verify the pattern with at least three consecutive terms before committing.
• Forgetting interleaved (alternating) series — when no single pattern fits, immediately check odd and even positions separately.
• Confusing Z=26 with reverse alphabet Z=1 — read the question carefully, especially in letter series.
• In wrong term questions, correcting the term mentally but then marking the position number instead of the term's value as the answer.
• Spending more than 60 seconds on one series question — if stuck after one minute, skip and return. Series rarely reward extra time spent.

• EJOTY = E(5) J(10) O(15) T(20) Y(25) — memorise this string to quickly find alphabet positions without counting from A.
• ADD-MUL-SQ-CU-INTER: the 5-step checklist to run through any number series in order — Additive, Multiplicative, Squares, Cubes, Interleaved.
• SPLIT and SOLVE for mixed series — split letters from numbers, solve each, rejoin. Think of it like separating egg yolk from white.
• Wrong term = ODD ONE OUT in disguise — use the same elimination mindset as classification questions.

• SSC CHSL typically gives 3 to 5 series questions per paper. They are placed early in the Reasoning section and are considered easy to medium — do these first to build speed and confidence.
• Number series is slightly more common than letter series in recent CHSL papers (2022-2024). Interleaved and square/cube patterns have appeared repeatedly in recent Tier 1 papers.
• Wrong term series questions appear at least once per paper — practice spotting the deviation quickly rather than recalculating the entire series.
• Time target: 30 to 45 seconds per series question. If you know the pattern type instantly, 20 seconds is achievable. Anything over 75 seconds — move on.
• Mixed alphanumeric series appear more in DEO-level papers. If your target is LDC, focus more on pure number and letter series patterns first.