Classification (Odd One Out)

Overview & Fundamental Concept

Comprehensive AISSEE Class 6 Intelligence guide for Classification (Odd One Out). Covers word classification, prime numbers vs composites, digit sum divisibility, letter cluster intervals, figural symmetry, solved models, and 10 practice drills.

• Classification (Odd One Out) requires analyzing four given terms, discovering the single unifying property shared by three of them, and identifying the one term that does NOT belong to this group.
• 1. Biological Taxonomy (Animal & Plant Kingdoms):
• • Mammals vs Non-Mammals: Bat, Whale, Dolphin, Human are Mammals (give live birth, produce milk). Frog (Amphibian), Snake (Reptile), Eagle (Bird) are non-mammals. (Bat is NOT a bird; Whale is NOT a fish!).
• • Herbivores vs Carnivores vs Omnivores: Cow, Deer, Goat (Herbivores) vs Lion, Tiger, Leopard (Carnivores).
• • Amphibians vs Reptiles: Frog, Toad, Salamander (Amphibians) vs Lizard, Snake, Crocodile, Turtle (Reptiles).
• 2. Geographical Categories:
• • Continents vs Countries vs Oceans: Asia, Africa, Europe (Continents) vs Australia (both) vs Pacific (Ocean).
• • Landlocked vs Coastal Nations / States: Nepal, Bhutan, Switzerland (Landlocked) vs India, Sri Lanka (Coastal).
• • Rivers vs Lakes vs Seas: Nile, Amazon, Ganga (Flowing rivers) vs Caspian, Superior (Lakes).
• 3. Physical Science & Materials:
• • Metals vs Non-Metals: Iron, Copper, Gold, Silver (Metals) vs Carbon, Oxygen, Sulphur (Non-metals).
• • Mercury Anomaly: Mercury is the ONLY metal that is liquid at room temperature; Bromine is the only liquid non-metal.

• Numerical classification tests fundamental arithmetic and algebraic number theory properties:
• 1. Prime vs Composite Number Test (Examiners' Top Choice!):
• • Primes: Numbers with exactly two factors (1 and itself): 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.
• • Example: Among 29, 31, 37, 39 -> 39 is the odd one because $39 = 3 imes 13$ (composite), while the others are primes.
• 2. Powers: Perfect Squares and Perfect Cubes:
• • Example: 64, 125, 216, 343 -> 64 is both a square ($8^2$) and a cube ($4^3$). But 125 ($5^3$), 216 ($6^3$), 343 ($7^3$) are pure cubes.
• 3. Divisibility Rules & Digital Sums:
• • Divisibility by 3 or 9: Sum of digits is divisible by 3 or 9.
• • Divisibility by 11: Difference between sum of odd-place digits and sum of even-place digits is 0 or multiple of 11.
• 4. Even / Odd Parity: Least preferred rule; only use if prime, power, and divisibility patterns fail.

• Letter group classification questions present four 3-letter or 4-letter clusters (e.g. BDF, HJL, PRT, WYA):
• 1. Positional Interval / Skip Patterns: Compute the difference between consecutive letters using their forward ranks:
• • BDF: $B(2) \xrightarrow{} D(4) \xrightarrow{} F(6)$ (Consistent $+2$ pattern).
• • HJL: $H(8) \xrightarrow{} J(10) \xrightarrow{} L(12)$ ($+2$ pattern).
• • PRT: $P(16) \xrightarrow{} R(18) \xrightarrow{} T(20)$ ($+2$ pattern).
• • WYA: $W(23) \xrightarrow{} Y(25) \xrightarrow{} A(1/27)$ ($+2$ pattern).
• 2. Vowel-Consonant Distribution:
• • Check the presence and number of vowels ($A, E, I, O, U$). A cluster with zero vowels or two vowels stands out as the odd one.
• 3. Reverse Opposite Pair Clusters:
• • Clusters formed by reverse pairs: $AZ, BY, CX, DW$. If one cluster is $EV$ and another is $HS$, an option like $JK$ (not a pair) is the outlier.
• 4. Cumulative Rank Sums: The sum of letter ranks in three options equals an even number or a specific multiple.

• In non-verbal classification, four geometric figures are presented, and the unique outlier must be identified:
• 1. Lines of Symmetry Test: Count axes of reflective symmetry. A circle has infinite; a square has 4; an equilateral triangle has 3; a scalene triangle has 0.
• 2. Closed vs Open Figures: Three figures are completely enclosed polygons, while one has a tiny opening or disconnected boundary.
• 3. Number of Component Line Segments: Count the lines forming each figure (e.g. three figures have 4 lines, one has 5 lines).
• 4. Rotational Chirality (Clockwise vs Counter-Clockwise): Arrows or pinwheels rotating CW vs CCW.
• 5. Shading / Partition Symmetry: Symmetrical bisecting line vs asymmetrical partition.