Coding-Decoding for the Assam Police Constable (AB & UB) Exam
Coding-Decoding is a scoring topic of the reasoning paper in the SLPRB Assam Police Constable (AB & UB) examination. A word, a number or a group of letters is written in a secret form, called the code, and the candidate must find the rule by which the code was made and then apply it to a new word. The questions need no general knowledge and no long calculation, only careful observation of the change between the code and the word. Once the rule is found the whole question is solved in a few seconds. This page explains the common codes, shows worked examples, gives a step by step method and lists the traps that cost marks. The material follows the standard reasoning reference books used for Assam recruitment examinations and is reviewed before it is published.
What the Topic Means
Coding means writing a word in a secret form by a fixed rule, and decoding means recovering the original word from that form. In the examination one coded example is usually given with its original, and the candidate must apply the same rule to a second word. The rule may be a shift of the letters, a reversal of the order, a substitution, a change of positions or a mixture of these.
Common Types of Coding
- Letter shifting: each letter is moved forward or backward by a fixed number of places, so CAT may become DBU when every letter is moved one place forward.
- Reversal: the whole word is written backwards, so CAT becomes TAC.
- Position coding: each letter is given the number of its position, so CAT becomes 3, 1, 20.
- Substitution: a fixed letter is used in place of another, such as a rule that replaces each vowel with the next letter.
- Interchange: the first and the last letters are swapped, or the letters are rearranged in pairs.
- Number coding: letters are given arbitrary numbers, which must be found from the given example.
- Conditional coding: a condition about the word decides the code, such as treating the first and last letters differently.
A Step by Step Method
- Write the given word above the given code, letter by letter, so the two can be compared.
- Find the change in the first letter and check whether the same change repeats in the other letters.
- If the letters shift, note the number of places and the direction.
- If the order changes, note which positions are swapped or reversed.
- Apply the same rule to the new word and check the answer against all the choices.
Worked Examples
Suppose TEACHER is written as UFBDIFS. Comparing the two, each letter has moved one place forward, since T becomes U, E becomes F and so on. So SCHOOL would be written as TDIPPM, moving each letter one place forward. In another example, if MOTHER is written as REHTOM, the word has simply been reversed, so FATHER becomes REHTAF. In a third example, if 6 is used for the first letter, 5 for the second and so on, the code is the reverse position of each letter, and the candidate must use that rule for the new word.
How This Topic Appears in the Examination
The topic usually appears as two to four objective questions of one mark each. The common forms are to find the code of a given word, to find the word from a given code, and to find the number code of a word. The questions are quick and reward a candidate who writes the letter by letter comparison neatly.
Shortcuts and Speed Methods
- Always write the word and the code one below the other before hunting for the rule.
- Check the shift on the first letter and confirm it on the last letter.
- If the shift is not fixed, check whether the shift grows or changes direction in the middle of the word.
- For number codes, write the alphabet positions below the letters.
- Eliminate choices that do not obey the rule found.
Common Mistakes to Avoid
- Assuming one rule from the first letter without checking the whole word.
- Confusing forward and backward shifts.
- Mixing the alphabet position with the reverse position.
- Forgetting that some codes change direction in the middle.
- Marking the answer before checking it against all the choices.
Preparation Plan
- Learn the alphabet positions and the reverse positions.
- Practise writing the word and the code one below the other for every question.
- Solve a set of ten questions daily, mixing shifts, reversals and number codes.
- Revise the common types listed on this page.
- Solve the coding questions of previous Assam Police papers.
More Practice Questions
- If PEN is written as QFO, each letter has moved one place forward, so INK is written as JOL.
- If ROSE is written as ESR0 with a reversal, then the reversal of LILY is YLIL.
- If RAM is written as 18, 1, 13, the code uses the alphabet position, so SITA is 19, 9, 20, 1.
- If the first and last letters are swapped, then GREAT becomes TEARG.
- If each vowel is changed to the next letter and each consonant is kept, then BALL becomes BCLL.
Quick Revision Checklist
- Letter shifting forward and backward.
- Reversal and interchange of positions.
- Position codes and arbitrary number codes.
- Conditional and mixed codes.
- Always compare the word and the code letter by letter.
Frequently Asked Questions
What is coding-decoding?
Coding-decoding is a reasoning topic in which a word is written in a secret form by a fixed rule, and the candidate must find the rule and apply it to a new word.
What is the first step in solving a coding question?
Write the given word and its code one below the other, letter by letter, and compare the first letter to find the change.
What is an interchange code?
In an interchange code the positions of letters are changed, such as swapping the first and last letters or reversing the whole word, without changing the letters themselves.
How do I handle a number code?
Write the alphabet position of each letter below it and compare with the given number code, then use the same rule for the new word.
Is coding-decoding easy to score?
Yes. Once the rule is found the question is solved quickly, and with a little practice most coding questions become sure marks.