Coding and decoding for SSC CGL

Coding–decoding is one of the most dependable scoring areas in SSC reasoning. You are shown a word and its code, and you must find the rule and apply it to a new word. There is no hidden knowledge involved. The only things that go wrong are a miscounted letter and a rule you assumed instead of checked.

Candidates who score full marks here do the same three things every time: they write positions, they compare letter by letter, and they check the rule on the whole word before touching the options.

How it appears in SSC CGL

Coding questions turn up in the reasoning sections of both Tier 1 and Tier 2. The count varies from shift to shift. The formats are steady:

Set up your rough sheet

Before the first question, write the alphabet with positions:

A1 B2 C3 D4 E5 F6 G7 H8 I9 J10 K11 L12 M13 N14 O15 P16 Q17 R18 S19 T20 U21 V22 W23 X24 Y25 Z26

Add two memory hooks. Opposite letters add to 27: A–Z, B–Y, C–X, and so on. And the word EJOTY marks positions 5, 10, 15, 20 and 25, so you can find any letter in two steps. Shifts wrap around: one step after Z is A.

The solving method

1. Write the word and its code in two rows, with positions under each letter.
2. Find the change for each letter: +1, −2, +1 then +2, and so on.
3. No steady change? Compare the code with the reversed word, then check opposites.
4. For number codes, test positions, sums and products, or build a letter-to-digit key.
5. Apply the rule to the question word, then match an option. Never pick the option that merely looks close.

Six worked examples

1. PENCIL is coded QFODJM. How is ERASER coded?

P16 → Q17, E5 → F6, N14 → O15, C3 → D4, I9 → J10, L12 → M13. Every letter moves +1. ERASER: E→F, R→S, A→B, S→T, E→F, R→S = FSBTFS.

2. GOLD is coded HQOH. How is SILK coded?

G7 → H8 (+1), O15 → Q17 (+2), L12 → O15 (+3), D4 → H8 (+4). The shifts rise by one. SILK: S19 + 1 = 20 (T), I9 + 2 = 11 (K), L12 + 3 = 15 (O), K11 + 4 = 15 (O) = TKOO.

3. STAR is coded SBUT. How is MOON coded?

Letter by letter, S→S, T→B, A→U, R→T gives shifts of 0, +8, +20, +2, which makes no sense. So test reversal. STAR reversed is RATS. RATS → SBUT is +1 on every letter. The rule: reverse, then shift +1. MOON reversed is NOOM, and +1 gives OPPN.

4. CAT is coded XZG. How is DOG coded?

C3 + X24 = 27, A1 + Z26 = 27, T20 + G7 = 27. Each letter is replaced by its opposite. DOG: D4 → W23, O15 → L12, G7 → T20 = WLT.

5. ROSE = 6821, CHAIR = 73456 and PREACH = 961473. Find the code for SEARCH.

Build a key from the first two words: R 6, O 8, S 2, E 1, C 7, H 3, A 4, I 5. PREACH confirms it (R 6, E 1, A 4, C 7, H 3) and adds P 9. SEARCH = S E A R C H = 214673.

6. In a code, "pit ka tom" means "sun is hot", "tom ro sa" means "hot and humid" and "ka ne pit" means "sun is bright". What is the code for "bright" and for "hot"?

Sentences 1 and 3 share "sun is", and their codes share "pit ka". So "ne" = bright. Sentences 1 and 2 share "hot", and their codes share "tom". So "tom" = hot.

Note what you can't find: whether "pit" means "sun" or "is". If a question asks for that, the answer is "cannot be determined", and it is often one of the options.

Substitution: answer with the code word

"If sky is called sea, sea is called water, water is called air and air is called cloud, where do fish live?" Fish live in water, and water is called air. The question asks what the thing is called, so give the substituted name, never the real one.

Common mistakes

Practice

1. TABLE is coded UBCMF. How is CHAIR coded?
   • (a) DIBJS (b) DIBJT (c) BGZHQ (d) DHBJS
2. APPLE is coded ELPPA. How is ORANGE coded?
3. MAN is coded NZM. How is WOMAN coded?
   • (a) DLNZM (b) XNLZM (c) DLMZN (d) DKNZM
4. If BAD = 7, what is FEED?
5. If white is called blue, blue is called red and red is called yellow, what is the colour of a clear sky?
6. FISH is coded EHRG. How is WATER coded?
7. In a code, "go home now" is "la pa ta", "now or never" is "ta ri si" and "come home" is "pa ko". What is the code for "go"?
8. BAD is coded 4 2 8. How is FACE coded?
   • (a) 12 2 6 10 (b) 7 2 4 6 (c) 12 1 6 10 (d) 36 1 9 25

Answers

1. (a) DIBJS. T→U, A→B, B→C, L→M, E→F is +1 throughout. CHAIR becomes D, I, B, J, S.
2. EGNARO. APPLE is simply written backwards.
3. (a) DLNZM. MAN → NZM swaps each letter for its opposite: M (13) ↔ N (14), A ↔ Z, N ↔ M. W ↔ D, O ↔ L, M ↔ N, A ↔ Z, N ↔ M.
4. 20. BAD = 2 + 1 + 4 = 7, a sum of positions (the product, 8, does not fit). FEED = 6 + 5 + 5 + 4 = 20.
5. Red. A clear sky is blue, and blue is called red.
6. VZSDQ. Each letter moves −1: W→V, A→Z (wrap-around), T→S, E→D, R→Q.
7. la. "home" is in sentences 1 and 3, and "pa" is common to their codes, so pa = home. "now" is in 1 and 2, and "ta" is common, so ta = now. That leaves la = go.
8. (a) 12 2 6 10. Each number is twice the letter's position: B2 → 4, A1 → 2, D4 → 8. F6 → 12, A1 → 2, C3 → 6, E5 → 10.

What to do next

1. Write the A1 to Z26 row and the opposite pairs from memory each morning for a week, timing yourself.
2. Solve 15 coding questions a day and write the rule type beside each one. Aim for a mix of all seven types.
3. When you miss one, redo it the next day without looking at the solution.
4. Coding uses the same position skills as number and letter series. The symbol-swap cousin of this topic is mathematical operations.