Coding-Decoding: Letter Shifting, Number and Symbol Coding

Letter shifting codes

Each letter moves a fixed number of places in the alphabet. Example: CAT → DBU (+1 each). Always write the positions: A=1 … Z=26, and use EJOTY (5, 10, 15, 20, 25) to find positions fast.

Reverse-alphabet codes

A ↔ Z, B ↔ Y … The pair always adds to 27. So the code of M (13) is N (14).

Number coding

Letters are replaced by their positions or by a sum. Example: if BAD = 7 (2+1+4), then CAB = 3+1+2 = 6.

Symbol / sentence coding

In "sky is blue = ka pa ta", "blue is red = pa ta na": the common words (is, blue) share the common codes (pa, ta). Compare sentences two at a time to isolate each word.

Exam tips

1. Check the first two letters to guess the rule, then verify on the last letter.
2. For sentence codes, eliminate common words first.

Analogy

Coding-decoding is like a secret handshake. Once you notice the pattern — two taps, one shake — you can repeat it with anyone. Find the rule on one word and apply it to every other word.