Coding‑Decoding – FCI Recruitment (Reasoning Ability)
What you’ll learn
• What coding‑decoding questions are
• How to spot patterns and decode quickly
• Common coding schemes (alphabetic, numeric, symbol, word‑based)
• Step‑by‑step solving strategy
• A full worked example
• A quick revision checklist
1. Simple Explanation
Coding‑decoding is a sub‑type of reasoning where you are given a set of symbols (letters, numbers, shapes, or words) and you must find the rule that transforms one symbol into another.
- Coding: Convert a given symbol into its coded counterpart.
- Decoding: Convert a coded symbol back into its original form.
Example:
If the code rule is “add 3 to the alphabet position”, then A → D, B → E, etc.
In exams you usually have:
| Part | Task |
|---|---|
| A → B | Find rule |
| B → C | Apply rule |
| C → D | Code new symbol |
The goal is to deduce the rule in the first step and then use it in subsequent steps.
2. Key Points
| # | What to Watch For | Why It Matters |
|---|---|---|
| 1 | Alphabetic shift (A→D, Z→C). | Most common; start here. |
| 2 | Reverse order (A→Z, B→Y). | Simple reverse coding. |
| 3 | Alternating pattern (odd/even positions). | Look for two interleaved sequences. |
| 4 | Numeric equivalents (A=1, B=2, ...). | Often combined with other operations. |
| 5 | Arithmetic on positions (×2, +5, –3). | Basic operations are frequent. |
| 6 | Word‑based coding (first/last letter, vowel‑consonant swap). | Appears in “word coding” questions. |
| 7 | Symbol/Shape coding (circle→square). | Less common but still present. |
| 8 | Multiple rules (two rules applied in succession). | Be prepared for compound transformations. |
| 9 | Check consistency (apply to all pairs). | Confirms the rule. |
| 10 | Time management (1–2 min per question). | FCI tests are time‑pressured. |
3. Worked Example
Question
A → G
B → H
C → I
Find the code for the letter E.
Step 1 – Identify the Rule
| Given | Coded | Alphabet Position |
|---|---|---|
| A (1) | G (7) | +6 |
| B (2) | H (8) | +6 |
| C (3) | I (9) | +6 |
Rule: Add 6 to the alphabet position (i.e., shift forward by 6).
Check:
- D (4) → +6 → 10 → J
- E (5) → +6 → 11 → K
Step 2 – Apply to E
E is the 5th letter.
5 + 6 = 11 → K
Answer: K
Why it works
- All pairs follow the same +6 shift.
- No alternative pattern fits all three given pairs.
- The rule is simple and uses basic arithmetic.
4. Quick Revision Summary
| # | Topic | Quick Hint |
|---|---|---|
| 1 | Alphabetic shifts | +X, –X, reverse |
| 2 | Numeric mapping | A=1, B=2 … +/– operations |
| 3 | Alternating sequences | Odd/even positions |
| 4 | Word coding | First/last letter, vowels, consonants |
| 5 | Multiple rules | Apply rule 1 then rule 2 |
| 6 | Consistency check | Verify with all given pairs |
| 7 | Time strategy | 45 s for 4–6 pairs, 30 s for 2–3 pairs |
| 8 | Practice tip | Use flashcards with random pairs to train pattern spotting |
Final Tips for FCI
- Read all pairs first – sometimes the rule is hidden in the last pair.
- Write down alphabet positions – converting letters to numbers makes arithmetic obvious.
- Spot common patterns – shift, reverse, multiplication, addition of a constant.
- Eliminate – if a rule works for all given pairs, it’s almost certainly correct.
- Answer quickly – once the rule is known, coding/decoding is instantaneous.
Good luck with your preparation!