Coding–Decoding (Reasoning Ability – UP TET)
Coding‑decoding problems test your ability to spot relationships between words, letters, numbers or symbols and convert one into the other.
They are common in the UP TET Reasoning section, usually appearing as a set of 4–5 items followed by a “find the missing element” question.
1. Simple Explanation
| Term | What it means |
|---|---|
| Coding | Converting an element (word/letter/number) into a code (another word/letter/number). |
| Decoding | Reversing the code to obtain the original element. |
| Pattern | The consistent rule that links the coded and decoded pairs. |
| Cipher | A type of coding where letters are replaced by other letters or symbols. |
Goal: Identify the rule that links the given pairs, then apply it to solve the question.
2. Key Points & Strategies
| # | Strategy | How to Apply |
|---|---|---|
| 1 | Look for positional relationships | Count positions of letters in the alphabet, or digits in a number. |
| 2 | Check for arithmetic operations | Addition/subtraction of fixed values, multiplication, division. |
| 3 | Check for letter‑to‑number conversions | A=1, B=2, …, Z=26; then sum, product, or difference of these values. |
| 4 | Pattern of vowels/consonants | Sequence of vowels, or alternate consonant/vowel. |
| 5 | Use of word length or number of letters | The code might be the number of letters, or the reverse of the word. |
| 6 | Check for “reverse” or “mirror” | Reverse order of letters or digits. |
| 7 | Cyclic patterns | After a certain number of steps, the pattern repeats (e.g., 1,2,3,1,2,3…). |
| 8 | Substitution based on word meaning | “SUN – 12” (S=19, U=21, N=14 → 19+21+14=54, 5+4=9, 9=I, etc.). |
| 9 | Cross‑referencing multiple pairs | Use all given pairs to confirm a rule; avoid making decisions on one pair alone. |
| 10 | Check for “+”, “–”, “x”, “÷” symbols | Might indicate operations between letters/words. |
Tips for Quick Solving
- Write the pairs in a table – makes it easier to spot patterns.
- Calculate letter‑to‑number values for all letters in the word.
- Try the most common operations (sum, difference, product) before inventing a complex rule.
- If stuck, test a simple rule (reverse, +1, +2) and see if it satisfies all pairs.
- Always verify that the rule works for all given pairs before applying it to the unknown.
3. Worked Example
Question
| CODING | DECODING |
|---|---|
| JAVA | 11 |
| MANGO | 23 |
| PEAR | 7 |
| BREAD | ? |
Find the coding for BREAD.
Step 1: Convert letters to numbers
A=1, B=2, …, Z=26.
| Word | A=1 | B=2 | C=3 | … | Z=26 |
|---|---|---|---|---|---|
| JAVA | 10 | 1 | 22 | 1 | |
| MANGO | 13 | 1 | 14 | 7 | 15 |
| PEAR | 16 | 5 | 1 | 18 | |
| BREAD | 2 | 18 | 5 | 1 | 4 |
Step 2: Observe the “Decoding” numbers
- JAVA → 11
- MANGO → 23
- PEAR → 7
We need a rule that transforms the word to the given number.
Step 3: Test simple operations
Calculate the difference between the first and last letter (numeric values):
| Word | First (F) | Last (L) | F – L |
|---|---|---|---|
| JAVA | 10 | 1 | 9 |
| MANGO | 13 | 15 | –2 |
| PEAR | 16 | 18 | –2 |
The differences don’t match the decoding numbers.
Step 4: Try sum of letter values
| Word | Sum |
|---|---|
| JAVA | 10+1+22+1 = 34 |
| MANGO | 13+1+14+7+15 = 50 |
| PEAR | 16+5+1+18 = 40 |
No.
Step 5: Try sum of vowels only
| Word | Vowels | Sum |
|---|---|---|
| JAVA | A, A → 1+1 = 2 | |
| MANGO | A, O → 1+15 = 16 | |
| PEAR | E, A → 5+1 = 6 |
Again no.
Step 6: Try product of first and last letters
| Word | F × L |
|---|---|
| JAVA | 10×1 = 10 |
| MANGO | 13×15 = 195 |
| PEAR | 16×18 = 288 |
No.
Step 7: Try difference between product of first two letters and product of last two letters
(This is often a pattern in TET.)
| Word | (F1×F2) – (L1×L2)