Coding and Decoding Exit
Logical reasoning

Coding and Decoding

Find the rule from the one example, then test it on a second letter before you trust it. Most codes are a shift, a reversal, or a position-sum.

Start with this

If CAT is written as DBU, each letter moved one step forward. Coding questions hide a simple rule like that; your job is to find it and apply it.

Coding appears in almost every reasoning section. Most codes are one of four kinds: shift, reverse, opposite letter, or position number.

The four common codes

Shift: every letter moves the same number of steps (CAT → DBU is +1). The shift can also change per letter (+1, +2, +3 ...).

Reverse: the word is written backwards, sometimes with a shift too.

Opposite: each letter becomes its mirror in the alphabet (A <→ Z, B <→ Y). Pairs always add to 27.

Numbers: letters become their positions (CAT → 3 1 20), or the sum of positions.

A126B225C324D423E522F621G720H819I918J1017K1116L1215M1314N1413O1512P1611Q1710R189S198T207U216V225W234X243Y252Z261
Letter positions: A=1 ... Z=26 (reverse position underneath). Opposite pairs add to 27

Worked example

If MOTHER is coded as NPUIFS, how is FATHER coded?

  1. M → N, O → P, T → U: each letter +1.
    Why: Compare letter by letter.
  2. FATHER +1 = GBUIFS.

Answer: GBUIFS

Worked example

If GOLD is coded as TLOW, how is SILK coded?

  1. G (7) → T (20): 7 + 20 = 27. O → L: 15 + 12 = 27.
    Why: Opposite letters add to 27.
  2. SILK → HROP.

Answer: HROP

Worked example

If CAT = 24, what is DOG?

  1. C + A + T = 3 + 1 + 20 = 24.
    Why: Sum of positions.
  2. D + O + G = 4 + 15 + 7 = 26.

Answer: 26

Sentence codes ('Chinese' coding)

You get several sentences and their codes. Words common to two sentences share a common code. Compare sentences in pairs and cross out what matches.

Worked example

'sky is blue' = 'ta na pa', 'blue is deep' = 'na ka ta', 'sky and sea' = 'pa ro mi'. What is the code for 'deep'?

  1. Sentences 1 and 2 share 'is' and 'blue', and codes 'ta' and 'na'.
    Why: Common words match common codes.
  2. Sentence 2's remaining word 'deep' matches its remaining code.
  3. 'ka'.

Answer: ka

Shortcut: Sentence code by overlap

Use it when: 'pit na sa' = you are good, 'na ho pit' = are you fine ...

  1. Words common to two sentences map to codes common to the same two sentences.
  2. Peel them off one at a time.

Sentence code by overlap: try it

'la pe ro' = sweet hot coffee, 'ro ki ne' = coffee is good, 'pe ne ta' = hot good tea. Code for 'good'?

  1. 'coffee' is in sentences 1 and 2; the only code in both is 'ro'.
  2. 'good' is in 2 and 3; the only code in both is 'ne'.

Answer: ne

Your turn medium

If GREEN is coded TIVVM (reverse alphabet), how is BLUE coded?

  1. B → Y, L → O, U → F, E → V.

Answer: YOFV

Your turn medium

If 'water' is called 'air', 'air' is called 'fire', and 'fire' is called 'sky', what do fish live in?

  1. Fish live in water, and water is called 'air'.

Answer: air

Your turn medium

If TEACHER is coded VGCEJGT, how is STUDENT coded?

  1. +2 each.

Answer: UVWFGPV

Your turn hard

If FRIEND is coded HUMJTK, how is CANDLE coded?

  1. F+2, R+3, I+4, E+5, N+6, D+7.
  2. Apply the same shifts to CANDLE.

Answer: EDRIRL

Recap

Now practise

7 questions with full solutions.

Open practice Back to the lesson