What is coding-decoding? Explain the different types with examples and the method of solving.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open in two lines. Coding-decoding hides a word, number or sentence by a fixed rule. The task is to find the rule from a given example and apply it to a new word.
2 · Draw the method. [Diagram: Write the word and its code → Write letter positions → Find the shift or pattern → Test it on every letter → Apply to the new word → Decode back to check]
3 · Letter-shift coding. MANGO → NBOHP: each letter +1. Shifts can also grow, as in PEN → QGQ (+1, +2, +3).
4 · Reverse and opposite-letter coding.
Reverse: SALT → TLAS; reverse then shift: PLATE → FUBMQ.
Opposite letters (places add to 27): GOOD → TLLW.
5 · Number coding. Letters become positions or their sums: CAT = 3 + 1 + 20 = 24, so COW = 3 + 15 + 23 = 41.
6 · Substitution and sentence coding.
Substitution: if milk is called oil, a cow gives 'oil'.
Sentence: the word common to two sentences has the code common to both.
7 · Use in competitive exams. Bank papers set sentence-coding sets; SSC, railway and placement tests use letter, reverse and number codes.
8 · Close in one line. Find the rule from the example, test it on every letter, and decode your answer back to check it.
Scoring tip: Write the alphabet positions above the letters in your answer; it shows the rule clearly and earns method marks.
