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Reverse Letter-Number

Reverse Letter-Number Coding replaces each letter with its mirror position in the alphabet, where A=26, B=25, C=24, ..., Z=1. This is essentially the Atbash cipher applied to numerical coding. The relationship is: coded position = 27 - original position.

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200+Practice Questions
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1-2 hoursHours to Master

What You'll Learn

Introduction & Overview Why This Matters How to Solve Pro Tips & Tricks
Shortcut Methods Common Mistakes Practice Worksheets Exam Importance

Introduction to Reverse Letter-Number

Reverse Letter-Number Coding replaces each letter with its mirror position in the alphabet, where A=26, B=25, C=24, ..., Z=1. This is essentially the Atbash cipher applied to numerical coding. The relationship is: coded position = 27 - original position.

Prerequisites

Alphabet positions (A=1 to Z=26) Mirror formula: mirror_position = 27 - original_position Memorization of reverse pairs Basic arithmetic
Why This Matters: Reverse Letter-Number Coding appears in 1-2 questions in SSC CGL and Banking PO exams. It tests understanding of alphabetical symmetry.

How to Solve Reverse Letter-Number Problems

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Step 1: Convert the given letter to its position number (A=1, B=2, ..., Z=26)

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Step 2: Calculate mirror position = 27 - original position

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Step 3: Convert the mirror position back to a letter

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Step 4: Apply this to each letter in the word

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Step 5: For decoding, use the same formula (it is its own inverse)

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Step 6: Verify the transformation is consistent for all letters

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Step 7: Present the coded or decoded word

Pro Strategy: Memorize the reverse pairs: 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. The sum of mirror pair positions is always 27.

Example Problem

Example 1: Code 'CAT' using reverse letter-number coding (A=26, B=25, ...). Solution: Step 1: C=3, A=1, T=20 Step 2: C: 27-3=24→X, A:27-1=26→Z, T:27-20=7→G Step 3: Coded word = XZG Answer: XZG Example 2: Decode 'XZG' using reverse letter-number coding. Solution: X=24→27-24=3→C, Z=26→27-26=1→A, G=7→27-7=20→T → CAT Answer: CAT

Pro Tips & Tricks

  • Memorize: 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
  • The middle pair: M(13) ↔ N(14)
  • Formula: Mirror letter = letter at position (27 - original position)
  • Opposite coding is an involution (applying twice returns original)
  • Vowels map to consonants: A(1)→Z(26), E(5)→V(22), I(9)→R(18), O(15)→L(12), U(21)→F(6)
  • Common words: CAT→XZG, DOG→WLT, SUN→HFM

Shortcut Methods to Solve Faster

If original letter is at position p, mirror is at 27-p
A (1) ↔ Z (26), difference = 25
B (2) ↔ Y (25), difference = 23
The pattern: first becomes last, second becomes second-last
For quick coding, write the alphabet forward and backward and match positions

Common Mistakes to Avoid

Using 26-n instead of 27-n (off by one error)
Forgetting that reverse coding applies to each letter individually
Confusing reverse coding with reverse order of letters
Not maintaining the same letter order after coding

Ready to Master Reverse Letter-Number?

Start with Worksheet 1 and work your way up to expert level! Each worksheet includes:

20 practice questions
Detailed solutions
Step-by-step explanations
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