Coding-Decoding Notes for SSC Exams

Coding-Decoding is one of the most scoring chapters of the Reasoning section in SSC CGL, CHSL, MTS and GD exams. A word, a number or a group of letters is converted into a secret form using a fixed rule, and you have to find that rule and apply it to a new word. Once you know the handful of patterns that SSC repeats, every question can be solved in under 30 seconds. These coding-decoding notes for SSC explain every pattern with tables, solved examples and practice questions.

What Is Coding-Decoding?

• Coding means converting a message into a hidden form using a rule.
• Decoding means finding the rule and converting the hidden form back into the original message.
• In exams, you are given one or two examples of a code and asked to code or decode a new word using the same rule.
• Two to four questions on this topic usually come in the Reasoning section of SSC Tier 1.

Step 1: Memorise the Alphabet Positions

Almost every letter-based question needs the position of a letter. Learn this table once and revise it daily.

A	B	C	D	E	F	G	H	I	J	K	L	M
1	2	3	4	5	6	7	8	9	10	11	12	13
N	O	P	Q	R	S	T	U	V	W	X	Y	Z
14	15	16	17	18	19	20	21	22	23	24	25	26

• EJOTY trick: E = 5, J = 10, O = 15, T = 20, Y = 25. From these five anchor letters you can find any other letter quickly.
• Opposite letter rule: the position of a letter from the left plus its position from the right is always 27. So the opposite of A is Z, B is Y, C is X, and M is N.

Types of Coding-Decoding

Type	Rule	Example
Forward or backward shifting	Every letter moves a fixed number of places ahead or behind	CAT → DBU (+1)
Alternate shifting	Shifts follow a pattern such as +1, −1, +1, −1	SMART → TLBQU
Opposite (mirror) letters	Every letter is replaced by its opposite (sum of positions = 27)	BAG → YZT
Reverse order	The word is written backwards	STUDENT → TNEDUTS
Letter to number	Letters are replaced by their position values	BAD → 2 1 4
Sum of positions	Positions of all letters are added	SSC → 19 + 19 + 3 = 41
Substitution	One object is called by the name of another	If air is called rain, birds fly in rain
Number-letter table	Digits are assigned to letters from given words	DELHI = 73541

Type 1: Forward and Backward Shifting

Compare the first letter of the word with the first letter of its code and note how many places it has moved. Check the same shift on the second letter to confirm the rule.

• If the letter goes past Z, continue from A. For example, Y + 2 = A.
• If the letter goes before A, continue from Z. For example, A − 1 = Z.

Example 1. If CAT is coded as DBU, how is DOG coded?
Each letter moves one place ahead: D → E, O → P, G → H. Answer: EPH.

Example 2. If MONEY is coded as LNMDX, how is HOUSE coded?
Each letter moves one place back: H → G, O → N, U → T, S → R, E → D. Answer: GNTRD.

Example 3. If ROSE is coded as TQUG, how is LILY coded?
Each letter moves two places ahead: L → N, I → K, L → N, Y → Z → A. Answer: NKNA.

Type 2: Alternate or Pattern Shifting

If the same shift does not work for every letter, check whether the shift changes in a pattern. Common patterns are +1, −1, +1, −1 and +1, +2, +3, +4.

Example 4. If a code writes SMART by shifting letters +1, −1, +1, −1, +1, what is the code?
S + 1 = T, M − 1 = L, A + 1 = B, R − 1 = Q, T + 1 = U. Answer: TLBQU.

Type 3: Opposite Letter Coding

Replace every letter by its opposite using the rule: new position = 27 − old position.

Example 5. Find the opposite-letter code of BAG.
B (2) → 25 = Y, A (1) → 26 = Z, G (7) → 20 = T. Answer: YZT.

Example 6. If CHAIR is written as XSZRI, how is TABLE written?
The pattern is opposite letters. T (20) → 7 = G, A → Z, B → Y, L (12) → 15 = O, E (5) → 22 = V. Answer: GZYOV.

Type 4: Reverse Order Coding

The word is simply written from right to left. This type is easy to spot because the code has the same letters as the word.

Example 7. If FAMILY is coded as YLIMAF, how is STUDENT coded?
Write STUDENT backwards. Answer: TNEDUTS.

Type 5: Letter to Number and Number to Letter

• Direct value: A = 1, B = 2 and so on. CAB is written as 3 1 2.
• Sum of values: CAB = 3 + 1 + 2 = 6, so DAD = 4 + 1 + 4 = 9.
• Reverse value: A = 26, B = 25 and so on. Then CAT = 24 + 26 + 7 = 57.

Example 8. If A = 1, B = 2 and so on, find the value of DEAF.
D + E + A + F = 4 + 5 + 1 + 6 = 16.

Type 6: Substitution (Naming) Coding

Here, common objects are given new names. Always answer using the new name of the object that fits the question.

Example 9. If sky is called water, water is called air, air is called rain and rain is called cloud, where do birds fly?
Birds fly in the air, and air is called rain. Answer: rain.

Type 7: Number Coding from Given Words

Two words with their number codes are given. Match the common letters to find the digit for each letter, then code the new word.

Example 10. If DELHI is coded as 73541 and CALCUTTA as 82589662, how is CALICUT coded?
From the codes: D = 7, E = 3, L = 5, H = 4, I = 1, C = 8, A = 2, U = 9, T = 6. Now CALICUT = C 8, A 2, L 5, I 1, C 8, U 9, T 6. Answer: 8251896.

Quick Tips to Solve Faster

• First check whether the code uses the same letters (reverse order or rearrangement) or different letters (shifting or opposite).
• Compare only the first two letters to find the rule, then confirm it on the last letter.
• If the letters of the code are the mirror of the word, use the sum-27 rule.
• For wrap-around questions, remember that Z is followed by A.
• In number-coding questions, write the digit under each letter and check repeated letters.

Quick Revision Points

• A = 1 to Z = 26, and EJOTY = 5, 10, 15, 20, 25.
• Opposite letters always add up to 27.
• Shifting can be forward, backward or in an alternate pattern.
• Reverse order means the word is written backwards.
• In substitution coding, answer with the new name, not the real name.

Practice Questions With Answers

1. If BOOK is coded as CPPL, how is PAGE coded?
   Answer: QBHF (every letter +1).
2. If CHAIR is written as XSZRI, how is TABLE written?
   Answer: GZYOV (opposite letters).
3. If CAB = 6, find the value of DAD.
   Answer: 9 (4 + 1 + 4).
4. If pen is called pencil, pencil is called book and book is called bag, what will you write with?
   Answer: pencil (a pen is called pencil).
5. If ROSE is coded as TQUG, how is LILY coded?
   Answer: NKNA (every letter +2, with Y followed by Z and A).
6. If DELHI = 73541 and CALCUTTA = 82589662, find the code of CALICUT.
   Answer: 8251896.
7. If MUMBAI is written as NVNCBJ, how is KOLKATA written?
   Answer: LPMLBUB (every letter +1).
8. Which letter is the opposite of M in the alphabet?
   Answer: N (13 + 14 = 27).
9. If A = 26, B = 25 and so on, find the value of CAT.
   Answer: 57 (24 + 26 + 7).
10. If FAMILY is coded as YLIMAF, how is DOG coded?
    Answer: GOD (reverse order).

How to Practise This Chapter

Solve five coding-decoding questions every day for one week, and note which type you get wrong. Then attempt the same chapter in a timed set from our practice papers and check how the topic appears in real exams on the previous year papers page. After this chapter, continue with Letter, Number and Series and Analogy.

Explore More SSC Subjects

SSC exams test many subjects, so connect this topic with the related subjects below:

• Quantitative Aptitude Notes
• English Notes
• General Awareness Notes
• Computer Knowledge Notes
• Stenography Notes
• All SSC subjects and notes

Frequently Asked Questions

What is coding-decoding in reasoning?

Coding-decoding is a reasoning topic in which a word, number or symbol is converted into a hidden form using a fixed rule. You have to find that rule from the given example and apply it to a new word.

How many questions come from coding-decoding in SSC exams?

Usually two to four questions come from coding-decoding in the Reasoning section of SSC CGL, CHSL, MTS and GD papers, although the exact number changes from year to year.

What is the easiest way to learn alphabet positions?

Learn the EJOTY anchors (E = 5, J = 10, O = 15, T = 20, Y = 25) and count forward or backward from the nearest anchor. Writing the A to Z table daily for a week also helps.

What is the opposite letter rule?

The opposite of a letter is found by subtracting its position from 27. For example, the opposite of D (4) is 27 − 4 = 23, which is W.

How do I identify the type of coding quickly?

Check whether the code uses the same letters as the word. If it does, it is a reverse or rearrangement type. If the letters are different, compare the first two letters to see whether it is a fixed shift, an alternate shift or the opposite-letter rule.

What happens when a shifted letter goes beyond Z?

The alphabet is treated as a circle. After Z the count starts again from A, so Y + 2 gives A and Z + 1 gives A.

Is substitution coding difficult?

No. In substitution coding, simply decide which real object answers the question, and then write the new name given to that object. Most mistakes happen when students write the real name.

Can I use the sum of positions in every question?

No. Use the sum method only when the question clearly asks for the value of a word or when the code is a number equal to the total of letter positions. In other cases, check shifting or opposite-letter patterns first.

How should I practise coding-decoding for SSC?

Solve five questions daily, write down the rule for every question and revise the types table once a week. Take timed sets later to improve speed.

How much time should I spend on one coding-decoding question?

Aim for 20 to 30 seconds per question. If you cannot find the rule in 30 seconds, mark the question and move on.

Are coding-decoding questions asked in Hindi medium papers too?

Yes. In Hindi medium papers the same patterns are asked using Hindi letters or English letters, so the logic remains the same.

What mistakes should I avoid in coding-decoding?

Do not assume the rule from a single letter, do not forget wrap-around after Z, and do not mix up the new name with the real name in substitution questions.

Is there negative marking for this chapter?

Negative marking applies to the Reasoning section as per the exam notification, so attempt only those questions where you are sure of the rule.