Series

Series

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Series questions in SSC CGL Reasoning test your ability to identify patterns in sequences of numbers, letters, or both. These questions appear in Tier 1 (2-3 questions) and are considered high-scoring if you can spot the pattern quickly.

Types of Series:

1. Number Series: 2, 5, 8, 11, ?
2. Letter Series: A, C, E, G, ?
3. Alphanumeric Series: A1, B2, C3, D4, ?
4. Mixed Series: Multiple patterns combined
5. Wrong Number Series: Find the odd one out

Common Number Patterns:

Pattern	Example	Rule
Addition	3, 7, 11, 15	+4 each
Subtraction	20, 17, 14, 11	-3 each
Multiplication	2, 6, 18, 54	×3 each
Division	72, 36, 18, 9	÷2 each
Squares	1, 4, 9, 16	n²
Cubes	1, 8, 27, 64	n³
Prime	2, 3, 5, 7, 11	prime numbers

⚡ SSC CGL Exam Tips:

• Always check if the difference/sum between consecutive terms is constant or changing
• Look at the last digit for multiplication-based patterns
• For letter series, convert to numbers (A=1, B=2) to spot patterns
• Mixed series often have two interleaved patterns
• Check prime numbers when other patterns don’t fit

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Detailed Pattern Recognition

Example 1: Arithmetic Progression Find the missing term: 5, 12, 19, 26, ? Common difference = 7 Next term = 26 + 7 = 33

Example 2: Geometric/Multiplication Pattern Find the missing term: 3, 9, 27, 81, ? Each term multiplied by 3 243 = 81 × 3

Example 3: Square/Cube Pattern Find the missing term: 1, 8, 27, 64, ? These are cubes: 1³, 2³, 3³, 4³, 5³ Missing = 5³ = 125

Example 4: Fibonacci-like Pattern Find the missing term: 1, 1, 2, 3, 5, 8, ? Each term = sum of previous two Next = 5 + 8 = 13

Letter Series with Position Values:

Assign numbers to letters: A=1, B=2, C=3, … Z=26

Example 1: A, D, G, J, ? A=1, D=4, G=7, J=10 Difference = 3 each Next: M (13) ✓

Example 2: Z, X, U, Q, ? Z=26, X=24, U=21, Q=17 Differences: -2, -3, -4, -5 Next: L (17-5 = 12) ✓

Alphanumeric Series Patterns:

Example: A1, C4, E9, G16, ? Letters: A, C, E, G — consecutive odd letters Numbers: 1, 4, 9, 16 — perfect squares (1², 2², 3², 4²) Next: I25 (5²) ✓

Common Tricky Patterns:

Type	Example	Pattern
Product of digits	12, 24, 48	1×2=2, 2×4=8, 4×8=32
Sum + Product	2, 3, 7	2+3=5, 2×3=6, 5+6=11
Prime ± 1	2, 4, 10	primes ± 1 or ×2
Twin series	1, 3, 4, 6	Two interleaved series
Reverse order	12, 21, 13, 31	Mirror/reverse pattern

⚠️ SSC CGL Common Mistakes:

1. Assuming constant difference when it actually changes
2. Missing the prime number pattern
3. Not converting letters to numbers when helpful
4. Overlooking mixed/interleaved patterns

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage with complex patterns and previous year SSC CGL patterns.

Complex Pattern Types:

Type 1: Two-Stage (Alternating Operation) Series The series alternates between two operations applied to each preceding term.

Example: 3, 5, 10, 12, 24, 26, ? Pattern: +2, ×2, +2, ×2 … 3+2=5, 5×2=10, 10+2=12, 12×2=24, 24+2=26 Next: 26×2 = 52 ✓

Type 2: Sum-Based Series with an Offset Each term is built from the sum of the two preceding terms, with a fixed adjustment.

Example: 12, 13, 27, 40, 67, ? Rule: add the two previous terms, then add 2 on alternate steps. 12+13=25, +2 → 27 13+27=40 27+40=67 40+67=107, +2 → 109 Next: 109 ✓

Type 3: Series with Fractions

Example: 1/2, 2/3, 3/4, 4/5, ? Pattern: numerator increases by 1, denominator increases by 1 Next: 5/6 ✓

Type 4: Power Series

Example: 2, 3, 5, 7, 11, 13, ? Pattern: Prime numbers Next: 17 ✓

Example: 1, 4, 27, 16, 125, ? Pattern: 1³, 2², 3³, 4², 5³, 6² Alternating: cubes (n³) for odd positions, squares (n²) for even positions, where the base increases by 1 each term Next: 6² = 36 ✓

Letter Series Advanced:

Pattern: Consecutive letters with skip

Example: AZ, BY, CX, DW, ? First letters: A, B, C, D — next is E Last letters: Z, Y, X, W — next is V EV ✓

Pattern: Position arithmetic with growing difference

Example: J, L, P, U, ? J(10), L(12), P(16), U(21) Differences: +2, +4, +5, +7 The next difference continues the growth (+9). 21+9 = 30, and positions cycle past 26 (27=A, 28=B, 29=C, 30=D) Next: D ✓

Wrong Number Series — Method: Compute the differences (or ratios) between consecutive terms and test them against a clean rule such as consecutive squares, cubes, or powers of 2. The term that breaks the otherwise consistent rule is the wrong number.

Worked check (a fully consistent series, no error): 2, 6, 15, 31, 56, 92 Differences: 4, 9, 16, 25, 36 — these are 2², 3², 4², 5², 6² 2+4=6, 6+9=15, 15+16=31, 31+25=56, 56+36=92 — every term fits, so this series is correct.

Worked check (powers of 2 added): 2, 6, 14, 30, 62, 126 Differences: 4, 8, 16, 32, 64 — successive powers of 2; the series is consistent.

Spotting the odd one out: 2, 3, 6, 15, 31, 127 Differences: 1, 3, 9, 16, 96. The first three (1, 3, 9) suggest a clean ×3 / square pattern, but 16 and 96 break it — the final term is the wrong number.

Previous Year SSC CGL Patterns:

SSC CGL 2022: Find the next term: 6, 12, 24, 48, ? a) 72 b) 96 c) 84 d) 60 Answer: b) 96 Pattern: ×2 each term. 48×2 = 96

SSC CGL 2022: Find the next term: A, E, I, M, Q, ? a) S b) T c) U d) V Answer: c) U A(1), E(5), I(9), M(13), Q(17) — all are 4 positions apart 17+4 = 21 = U ✓

SSC CGL 2023: Complete the series: BZD, EYG, HXJ, KWM, ? First letters: B, E, H, K — +3 each Middle letters: Z, Y, X, W — -1 each Last letters: D, G, J, M — +3 each Next: N (K+3=14=N), V (W-1=22=V), P (M+3=16=P) NVP ✓

Speed Strategies:

1. Calculate differences first — most series are based on arithmetic of differences
2. For letter series, always write position numbers (A=1, B=2…)
3. Check if terms are prime numbers
4. Look for squares/cubes nearby (1, 4, 9, 16, 25…)
5. In mixed series, separate odd and even position terms

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