Logical Reasoning · Micro-test

Coding-Decoding

Coding-decoding hides a fixed, mechanical rule behind an unfamiliar-looking word, and the entire task is reverse-engineering that rule from one clean example before applying it to a new word.

10 questions · 5 minutes · instant scoring

Updated 10 September 2026

What this topic actually tests

A coding-decoding question gives one or more example words alongside their coded form and asks you to find the code for a new word, or occasionally to decode a coded word back into plain English. The underlying rule is always fixed and mechanical, and it almost always falls into one of a few families: a constant letter shift, where every letter moves a fixed number of steps forward or backward in the alphabet (A becomes C, B becomes D, and so on for a +2 shift); a position-based numeric code, where each letter is simply replaced by its position in the alphabet (A=1 through Z=26); a reverse-alphabet substitution, where each letter is replaced by its mirror-image letter counted from the other end (A pairs with Z, B with Y, and generally a letter in position n pairs with position 27-n); and an increasing-shift code, where the first letter of a word shifts by 1, the second letter by 2, the third by 3, and so on. The critical discipline is to verify the rule against every letter of the given example before applying it to the new word, since a rule that works for the first two letters but not the third is the wrong rule. Worked example: if PAPER is coded as QCSIW, checking letter by letter shows P shifts by 1 to Q, A shifts by 2 to C, P shifts by 3 to S, E shifts by 4 to I, and R shifts by 5 to W - confirming an increasing-shift rule where the nth letter moves forward by n places, which can then be applied confidently to any new word.

The common trap on this topic

The most common CLAT mistake is locking onto a rule after checking only the first one or two letters of the example, then applying that unconfirmed rule to the new word and getting a plausible but wrong answer - the correct approach always verifies the rule against the entire given example, letter by letter, before trusting it. A second frequent trap is confusing a constant shift with an increasing shift; both can look identical on a short word's first couple of letters, so students must check whether the shift amount stays the same or grows with each letter's position. A third trap specific to reverse-alphabet codes is forgetting that the correct pairing formula is 27 minus the letter's position, not 26 minus it - miscounting this by one consistently shifts every decoded letter by one place and produces an answer that looks almost right but is systematically wrong throughout the whole word.

Coding-Decoding: answers and explanations

In a certain code, each letter is replaced by the letter two places ahead of it in the alphabet (A becomes C, B becomes D, and so on). How is the word LOGIC written in that code?
Answer: B. NQIKE
Shifting each letter of LOGIC forward by two places gives L to N, O to Q, G to I, I to K, and C to E, which spells NQIKE.
If WATER is coded as YCVGT, what is the code for EARTH in the same language?
Answer: C. GCTVJ
Checking WATER against YCVGT confirms every letter shifts forward by two places (W to Y, A to C, T to V, E to G, R to T). Applying the same +2 shift to EARTH gives E to G, A to C, R to T, T to V, and H to J, spelling GCTVJ.
In a certain code, MONEY is written as 13-15-14-5-25, using each letter's position in the alphabet. How is TIME written in the same code?
Answer: C. 20-9-13-5
The code simply gives each letter's position in the alphabet (M=13, O=15, N=14, E=5, Y=25). Applying this to TIME gives T=20, I=9, M=13, and E=5, so the code is 20-9-13-5.
In a code language, if RED is called BLUE, BLUE is called GREEN, and GREEN is called YELLOW, what colour is grass, which is normally green?
Answer: A. Yellow
Grass is normally green, and according to the given code chain, GREEN is called YELLOW. So in this code language, grass would be called yellow.
In a certain code, PAPER is written as QCSIW. How is PENCIL written in the same code?
Answer: B. QGQGNR
Checking PAPER against QCSIW shows the 1st letter shifts by 1, the 2nd by 2, the 3rd by 3, the 4th by 4, and the 5th by 5 (P+1=Q, A+2=C, P+3=S, E+4=I, R+5=W). Applying this increasing shift to PENCIL's six letters gives P+1=Q, E+2=G, N+3=Q, C+4=G, I+5=N, L+6=R, spelling QGQGNR.
If A is coded as 1, B as 2, and so on up to Z as 26, what is the code for CAT expressed as the sum of its letters' codes?
Answer: A. 24
C is 3, A is 1, and T is 20. Adding these gives 3 + 1 + 20 = 24.
In a certain code, GARDEN is written as TZIWVM, where each letter is replaced by its mirror-image letter counted from the other end of the alphabet (position n pairs with position 27 minus n). How is FLOWER written in the same code?
Answer: C. UOLDVI
The rule pairs each letter's position n with 27 minus n. Applying this to FLOWER: F(6) to 21=U, L(12) to 15=O, O(15) to 12=L, W(23) to 4=D, E(5) to 22=V, R(18) to 9=I, giving UOLDVI.
If letters are numbered A=1 through Z=26, and a word's code is formed by reversing the digits of each letter's number, what is the code for the letter M (13th letter)?
Answer: A. 31
M is the 13th letter. Reversing the digits of 13 gives 31, so the code for M is 31.
In a certain code, SUN is written as UWP and MOON is written as OQQP. What is the code for STAR in the same language?
Answer: C. UVCT
Both examples confirm a constant +2 shift for every letter (S to U, U to W, N to P; M to O, O to Q twice, N to P). Applying +2 to STAR gives S to U, T to V, A to C, and R to T, spelling UVCT.
In a code language, DOCTOR is written as EPDUPS and TEACHER is written as UFBDIFS. What is the code for STUDENT in the same language?
Answer: C. TUVEFOU
Both examples confirm a constant +1 shift for every letter (D to E, O to P, C to D, and so on). Applying +1 to STUDENT gives S to T, T to U, U to V, D to E, E to F, N to O, and T to U, spelling TUVEFOU.

FAQ

How can I tell if a coding rule is a constant shift or an increasing shift?

Compute the shift amount separately for each letter in the given example. If every letter moves by the same fixed number of places, it is a constant shift; if the shift amount itself increases with each letter's position in the word (1, 2, 3, and so on), it is an increasing-shift code.

What is the formula for a reverse-alphabet code?

A letter in position n of the alphabet is replaced by the letter in position 27 minus n, so A (1) pairs with Z (26), B (2) pairs with Y (25), and so on, always summing to 27.

Why should I check the entire example word instead of just the first letter?

Because a rule can coincidentally match the first letter or two by chance while being the wrong rule overall; verifying every letter against the given code confirms the rule is consistent and safe to apply to a brand-new word.

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