Series and Analogy

Why This Chapter Matters

Series (number, letter, mixed) and Analogy together give 6-10 marks in SSC CGL and CHSL. These are the most consistent questions — same pattern repeated every year.

Analogy (yes, about Analogy questions themselves) — Think of a word-analogy question like a recipe you're asked to repeat with different ingredients. "Tool : User" (Hammer : Carpenter) isn't really about hammers or carpenters specifically — it's about the RELATIONSHIP (an object and the person who characteristically uses it). Once you name the relationship precisely in your own words first ("X is the tool of profession Y"), applying that same relationship to a new pair of options becomes mechanical rather than another guess — the skill is extracting the relationship, not memorizing every possible word pair.

Part 1 — Number Series

Types of Series

Difference series: Find the pattern in differences.

2, 5, 10, 17, 26, ? → Differences: 3,5,7,9,11 (odd numbers) → next diff=11 → 26+11=37.

Ratio series: Each term = previous × fixed number.

3, 6, 12, 24, ? → ratio=2 → next=48.

Square/Cube series:

1, 4, 9, 16, ? → Perfect squares → 25.

2, 9, 28, 65, ? → (1³+1, 2³+1, 3³+1, 4³+1) → 5³+1=126.

Mixed operations:

5, 11, 23, 47, ? → ×2+1: 5×2+1=11, 11×2+1=23, 23×2+1=47, 47×2+1=95.

Two-step patterns:

+2, +4, +2, +4... | +1,+3,+1,+3... | alternating operations.

Approach: Find difference between consecutive terms. If differences have a pattern → done. If not, check ratio. If not, check second differences (differences of differences).

Common SSC Patterns

n² series: 1,4,9,16,25,36...

n²+1: 2,5,10,17,26...

n²-1: 0,3,8,15,24...

n(n+1): 2,6,12,20,30...

Fibonacci: 1,1,2,3,5,8,13,21...

Part 2 — Letter/Alphabet Series

Positions: A=1, B=2...Z=26. Or from end: A=26, Z=1.

Pattern: Find position differences.

A, C, F, J, ? → differences: 2,3,4,5 → next diff=5 → J(10)+5=15=O.

Reverse alphabet: Z=1, Y=2...A=26.

Letter pairs: AC, EG, IK, MO, ? → vowels +2 → QS.

Part 3 — Analogy

Word Analogy

Find the relationship in the first pair, apply to the second.

Doctor : Hospital :: Teacher : School (person : workplace)

Book : Library :: Money : Bank (things : where they are stored)

Hammer : Carpenter :: Stethoscope : Doctor (tool : user)

Eye : See :: Ear : Hear (organ : function)

Common relationships:

Tool-user | Part-whole | Worker-workplace | Thing-material

Animal-young | Animal-sound | Degree of intensity | Cause-effect

Opposite | Synonym | Country-capital | Country-currency

Number Analogy

16:4 :: 25:5 (perfect squares : square roots)

8:512 :: 5:125 (n:n³)

Find operation connecting pair 1, apply to pair 2.

Letter Analogy

ACE : FHJ :: KMO : ? → both skip one letter, shift +5 → PRT.

Solved Examples

Q1 (Series): 7, 12, 19, 28, 39, ?

Differences: 5,7,9,11 (adding 2 each time) → next diff=13 → 39+13=52.

Q2 (Analogy): Dog : Kennel :: Horse : ?

Dog lives in Kennel. Horse lives in Stable. Answer: Stable.

Q3 (Letter series): B, D, G, K, P, ?

Differences: 2,3,4,5,6 → P(16)+6=22=V. Answer: V.

PYQs (SSC)

SSC CGL 2023 (Series): 3, 7, 15, 31, 63, ?

Pattern: ×2+1 → 3×2+1=7, 7×2+1=15... → 63×2+1=127.

SSC CGL 2022 (Analogy): ACFJ : BDHK :: MOSX : ?

A+1=B, C+1=D, F+2=H, J+1=K. Pattern: +1,+1,+2,+1 → M+1=N, O+1=P, S+2=U, X+1=Y → NPUY.

Revision Notes

NUMBER SERIES APPROACH:
Step 1: Find differences | Step 2: If pattern → done
Step 3: If not, find ratio | Step 4: Check second differences
Step 5: Try n², n³, n(n+1) patterns

LETTER POSITIONS: A=1...Z=26 | From end: Z=1...A=26

ANALOGY RELATIONSHIPS:
Tool-User | Part-Whole | Worker-Workplace | Animal-Young
Animal-Sound | Country-Capital | Cause-Effect | Degree

COMMON OPERATIONS IN NUMBER ANALOGY:
n² | n³ | n(n+1) | 2n+1 | n+prime | n²+k

Try It (2 Minutes)

Given the analogy "Doctor : Hospital", state the relationship in one precise sentence before looking at the answer choices (e.g. "a professional and their characteristic workplace"). Now apply that exact same relationship to find the missing word in "Teacher : ___" — the answer should follow mechanically from your own stated rule (School), not from guessing among the options first. This "name the rule before touching the options" habit is what separates a 10-second analogy question from a 40-second one under real exam pressure.