Question 1

In a certain coding system, each letter is replaced by the letter that comes 3 positions after it in the English alphabet. For example, A is coded as D, B is coded as E, and so on. If a letter reaches beyond Z, it wraps around to the beginning (so X→A, Y→B, Z→C). Using this rule, what is the code for the word 'PLAY'?

Accepted Answer

Apply the +3 letter-shift rule to each letter in 'PLAY':

P (16th letter) + 3 = S (19th letter)
L (12th letter) + 3 = O (15th letter)
A (1st letter) + 3 = D (4th letter)
Y (25th letter) + 3 = wraps to B (25+3=28, 28-26=2, which is B)

Therefore, PLAY is coded as 'SODB'.

The answer is B.

Question 2

In a certain code language, each letter is replaced by the letter that comes 3 positions after it in the English alphabet. For example, A is coded as D, B is coded as E, and so on. Letters at the end of the alphabet wrap around (X→A, Y→B, Z→C). Using this coding system, what is the code for the word 'MOTHER'?

Accepted Answer

To solve this problem, we apply the +3 shift rule to each letter in 'MOTHER':

M (13th letter) → P (16th letter)
O (15th letter) → R (18th letter)
T (20th letter) → W (23rd letter)
H (8th letter) → K (11th letter)
E (5th letter) → H (8th letter)
R (18th letter) → U (21st letter)

Therefore, MOTHER is coded as PRWKHU.

Common mistakes:
- Option C (MRUIFQ): Incorrectly shifts by 2 positions instead of 3
- Option D (QSYHLX): Shifts some letters forward and some backward inconsistently
- Option A (PRIEHR): Applies the shift rule to only some letters, missing consistency

Question 3

In a certain coding system, each letter is replaced by the letter that comes 3 positions after it in the English alphabet, and the position wraps around (Z wraps to C). Using this rule, if the word TIGER is coded, what is the code?

Note: A=1, B=2, C=3, ... Z=26. After Z, the sequence wraps: A follows Z.

(A) WLJHU
(B) WLJHV
(C) XMKIV
(D) VKIGU

Accepted Answer

Setup: This question tests the ability to apply a consistent letter-shift cipher rule across all letters in a word, including handling the wrap-around case.

Solution:
The rule is: Replace each letter with the letter 3 positions after it (with wrap-around).

T = 20th letter → 20 + 3 = 23 → W
I = 9th letter → 9 + 3 = 12 → L
G = 7th letter → 7 + 3 = 10 → J
E = 5th letter → 5 + 3 = 8 → H
R = 18th letter → 18 + 3 = 21 → U

Therefore, TIGER → WLJHU

Trap Explanation: Option B (WLJHV) is the most tempting wrong answer. Students who correctly code T, I, G, E as W, L, J, H but then make an error on R are caught here. They might miscalculate R (18) + 3 = 21 (U) and instead think R maps to V (22), possibly by confusing the position or adding 4 instead of 3. This is a common arithmetic slip in shift ciphers.

Shortcut: Write out the alphabet with numbers 1-26. For each letter in TIGER, find its position, add 3, and locate the result. This eliminates guessing and ensures accuracy. Alternatively, memorise that T→W, I→L, G→J, E→H are the first four letters of the code, which uniquely identifies option A.

Question 4

In a coding system, each letter is replaced by a two-character code: the first character is the letter's position number in the alphabet (A=1, B=2, ..., Z=26), and the second character is the reverse position (A=26, B=25, ..., Z=1). Additionally, if a letter appears more than once in a word, every second occurrence onwards is prefixed with an asterisk (*). Decode the following: 1-26, 5-22, 12-15, 12-15*, 15-12, 23-4. What is the original word?

Accepted Answer

Setup: The code uses dual-position encoding (forward and reverse alphabet position) with asterisk markers for repeated letters. Solution: Decode each code pair: (1,26)=A, (5,22)=E, (12,15)=L, (12,15)*=L (second occurrence marked), (15,12)=O, (23,4)=W. The asterisk on the third code indicates this is the second occurrence of the letter L. Reading the decoded letters in sequence: A-E-L-L-O-W = ALLOW. Verification: A(1st pos=1, reverse=26)→1-26✓, L(1st=12, rev=15)→12-15✓, L(2nd occurrence gets *)→12-15*✓, O(1st=15, rev=12)→15-12✓, W(1st=23, rev=4)→23-4✓. Therefore, the original word is ALLOW, and the answer is B.

RRB Group D Coding Decoding

Coding Decoding— Rules & Concept

Key Points to Remember

Exam-Specific Tips

Coding Decoding — Practice Questions

60-Second Revision — Coding Decoding