Mental Ability — Complex Coding-Decoding, Matrix Coding, Conditional Coding

Coding-decoding is one of the most common reasoning topics in Kerala PSC exams. This note covers advanced patterns beyond simple letter shifts, including matrix coding, conditional coding, and mixed coding. 15 solved problems included.

Types of Coding-Decoding

Type	Description
Letter shifting	Each letter replaced by another letter at a fixed distance (e.g., +2: A=C, B=D)
Reverse order	Word reversed or letters reversed individually
Number coding	Letters replaced by numbers based on a pattern
Symbol coding	Letters/words replaced by symbols
Mixed coding	Combination of letter shift + reversal + number
Matrix coding	Letters encoded using row-column numbers from a matrix/grid
Conditional coding	Different rules applied based on conditions (position, vowel/consonant, etc.)
Sentence coding	Entire words replaced by codes; determine word-code pairs through comparison

Pattern 1: Variable Letter Shifting

Instead of a fixed shift, each position has a different shift value.

Rule example: 1st letter +1, 2nd letter +2, 3rd letter +3, and so on.

Problem 1: If COME is coded as DQPH, how is LOVE coded?

Solution:

• Pattern: C(3)+1=D(4), O(15)+2=Q(17), M(13)+3=P(16), E(5)+3=H(8). The shift is +1, +2, +3, +3.
• Applying to LOVE: L(12)+1=M(13), O(15)+2=Q(17), V(22)+3=Y(25), E(5)+3=H(8)
• Answer: MQYH

Problem 2: If BRAND is coded as CSBOE, how is PLANT coded?

Solution:

• B+1=C, R+1=S, A+1=B, N+1=O, D+1=E. Each letter shifted by +1.
• PLANT: P+1=Q, L+1=M, A+1=B, N+1=O, T+1=U
• Answer: QMBOU

Pattern 2: Reverse Alphabet Coding

Each letter replaced by its mirror in the alphabet: A=Z, B=Y, C=X, D=W … (A+Z=27, B+Y=27, etc.)

Formula: Code = 27 - Position

Problem 3: In a certain code, each letter is replaced by its opposite in the alphabet (A=Z, B=Y, C=X…). What is the code for TIGER?

Solution:

• T(20): 27-20=7=G
• I(9): 27-9=18=R
• G(7): 27-7=20=T
• E(5): 27-5=22=V
• R(18): 27-18=9=I
• Answer: GRTVI

Shortcut table for reverse alphabet:

A=Z	B=Y	C=X	D=W	E=V	F=U	G=T
H=S	I=R	J=Q	K=P	L=O	M=N	N=M

Pattern 3: Number-Letter Coding

Problem 4: If DELHI is written as 73598, how is HIDE written?

Solution:

• D=7, E=3, L=5, H=9, I=8
• HIDE: H=9, I=8, D=7, E=3
• Answer: 9873

Problem 5: If FACE = 6135 and CAFE = 3165, how is ACE coded?

Solution:

• From FACE: F=6, A=1, C=3, E=5
• From CAFE: C=3, A=1, F=6, E=5 (consistent)
• ACE: A=1, C=3, E=5
• Answer: 135

Pattern 4: Sentence/Word Coding

Problem 6: In a certain code:

• “sky is blue” = “ta pa na”
• “blue is bright” = “na sa pa”
• “sky is clear” = “ta pa ra”

What is the code for “blue”?

Solution:

• Compare sentences 1 and 2: common words “is blue” = common codes “na pa”
• Compare sentences 1 and 3: common words “sky is” = common codes “ta pa”
• From comparison: “is” = “pa” (common to all three)
• From sentence 1 and 2: “blue” = “na” (remaining common code after “is”=“pa”)
• Answer: na

Problem 7: In a certain code:

• “good and bad” = “1 2 3”
• “bad is ugly” = “3 4 5”
• “ugly and good” = “5 2 1”

What is the code for “is”?

Solution:

• “good and bad” = 1 2 3
• “ugly and good” = 5 2 1 (common: “good and” = “1 2”)
• So: good=1, and=2, bad=3
• “bad is ugly” = 3 4 5. bad=3, so is=4 or 5 and ugly=4 or 5
• From “ugly and good” = 5 2 1: ugly=5 (since good=1, and=2)
• Therefore: is=4
• Answer: 4

Pattern 5: Matrix Coding

In matrix coding, two matrices are given. Each letter can be represented by its row-column position.

Matrix 1:

	0	1	2	3	4
0	A	B	C	D	E
1	F	G	H	I	J
2	K	L	M	N	O
3	P	Q	R	S	T
4	U	V	W	X	Y

A letter is coded as (row, column). So A = 00, B = 01, G = 11, M = 22, Y = 44.

Problem 8: Using the matrix above, how is the word KING coded?

Solution:

• K = row 2, col 0 = 20
• I = row 1, col 3 = 13
• N = row 2, col 3 = 23
• G = row 1, col 1 = 11
• Answer: 20, 13, 23, 11

Problem 9: Using the same matrix, if a word is coded as 30, 24, 13, 23, 34, what is the word?

Solution:

• 30 = row 3, col 0 = P
• 24 = row 2, col 4 = O
• 13 = row 1, col 3 = I
• 23 = row 2, col 3 = N
• 34 = row 3, col 4 = T
• Answer: POINT

Pattern 6: Conditional Coding

Rules change based on conditions (e.g., vowel vs consonant, position in word).

Problem 10: Rules:

• Vowels are coded as the NEXT vowel (A=E, E=I, I=O, O=U, U=A)
• Consonants are coded as the NEXT consonant (B=C, C=D, …, Z=B)

How is BOAT coded?

Solution:

• B (consonant): next consonant = C
• O (vowel): next vowel = U
• A (vowel): next vowel = E
• T (consonant): next consonant = V
• Answer: CUEV

Problem 11: Rules:

• If a letter is at an ODD position in the word: code = letter + 2
• If a letter is at an EVEN position in the word: code = letter - 2

How is LAMP coded?

Solution:

• L (position 1, odd): L+2 = N
• A (position 2, even): A-2 = Y (wrap around: A is the 1st letter, going back 2 positions gives Y, the 25th letter)
• M (position 3, odd): M+2 = O
• P (position 4, even): P-2 = N
• Answer: NYON

Pattern 7: Symbol Substitution Coding

Problem 12: If + means multiply, - means divide, x means add, and / means subtract: What is 8 + 4 - 2 x 6 / 3?

Solution: Replace symbols: + becomes multiply, - becomes divide, x becomes add, / becomes subtract.

• 8 multiply 4 divide 2 add 6 subtract 3
• = (8 x 4) / 2 + 6 - 3
• = 32 / 2 + 6 - 3
• = 16 + 6 - 3
• = 19

Problem 13: If A = 1, B = 2, C = 3 … Z = 26, then what is the code value of KERALA?

Solution:

• K=11, E=5, R=18, A=1, L=12, A=1
• Sum = 11+5+18+1+12+1 = 48

Pattern 8: Mixed Operation Coding

Problem 14: In a coding system:

• First and last letters are swapped
• Middle letters are each shifted by +1

How is DREAM coded?

Solution:

• Original: D R E A M
• Swap first (D) and last (M): M R E A D
• Shift middle letters (R, E, A) by +1: S, F, B
• Result: M S F B D
• Answer: MSFBD

Pattern 9: Clock-Based Coding

Problem 15: In a code, each letter is assigned the number of the hour if we place A-L at positions 1-12 on a clock face (A=1, B=2 … L=12) and then M-X at 1-12 again (M=1, N=2 … X=12), and Y=1, Z=2.

How is MAP coded?

Solution:

• M = 1 (M is 13th letter; 13-12 = 1)
• A = 1
• P = 4 (P is 16th letter; 16-12 = 4)
• Answer: 1, 1, 4

Strategy Tips for PSC Exams

Tip	Details
Check for simple shift first	Try +1, +2, -1, -2 on the first two letters
Try reverse alphabet	If shift does not work, check mirror coding (A=Z pattern)
Position matters	Note whether the shift varies by position in the word
Sentence coding	Find common words between sentences to decode individual words
Matrix coding	Simply read row and column; practice reading quickly
Verify your answer	Always verify with the given code before choosing
Time management	Spend no more than 30-45 seconds per coding question

PSC Quick Recall

Pattern	Key Identifier
Simple shift	All letters moved by same fixed number
Variable shift	Each position has different shift (+1, +2, +3…)
Reverse alphabet	A=Z, B=Y, C=X pattern (sum = 27)
Sentence coding	Compare overlapping sentences to isolate word codes
Matrix coding	Two-digit row-column format
Conditional coding	Different rules for vowels vs consonants, or odd vs even positions
Symbol substitution	Mathematical operators swapped; solve with BODMAS after substitution