3.3 Coding and Decoding

Coding and Decoding

Quick Answer: Coding and decoding items give you a word and its code, then ask you to encode or decode a different word using the same rule. The two most common rule families are letter-shift ciphers, where every letter moves a fixed number of positions through the alphabet, and letter- or word-rearrangement rules, such as reversing spelling or swapping specific letters. Always figure out the exact rule from the given pair first, then apply it mechanically to the new word.

The Golden Rule: Derive First, Apply Second

The single biggest speed and accuracy gain on coding and decoding items comes from resisting the urge to guess the answer directly from the options. Instead, spend your first several seconds entirely on the given example, writing out exactly what changed from the original word to its code. Only after you can state the rule in one sentence should you apply it to the new word.

Letter-Shift Ciphers

A letter-shift cipher moves every letter the same fixed number of positions forward or backward through the alphabet.

Worked example: If CAT is coded as DBU, what is the code for DOG?

Compare each letter: C becomes D (forward one position), A becomes B (forward one position), T becomes U (forward one position). The shift is a constant plus one across the whole alphabet. Applying the same shift to DOG: D becomes E, O becomes P, G becomes H. The code for DOG is EPH.

Worked Example 2: A Larger Shift

If BIRD is coded as ELUG, what is the code for FISH?

Compare each letter of the given pair: B to E is forward 3 positions, I to L is forward 3, R to U is forward 3, and D to G is forward 3. The shift is a constant plus 3 across every letter. Applying that same shift to FISH: F becomes I, I becomes L, S becomes V, and H becomes K. The code for FISH is ILVK.

Always verify the shift on every letter of the given pair, not just the first one - a shift that looks consistent on the first letter but breaks on the second or third signals a different, non-shift rule instead.

Letter-Rearrangement and Substitution Rules

Not every code is a shift. Some rearrange or substitute letters using a fixed structural rule instead of moving through the alphabet.

Worked example: If STAR is coded as RATS, what is the code for LAMP?

Comparing STAR to RATS shows the letters are written in exactly reverse order (S, T, A, R becomes R, A, T, S). Applying the same reverse-order rule to LAMP: reversing L, A, M, P gives P, M, A, L. The code for LAMP is PMAL.

Worked Example 3: Number Codes From Alphabet Positions

Worked example: If CAB is coded as 312, what does this tell us, and what is the code for BAD?

Convert each letter of CAB to its alphabet position: C is 3, A is 1, B is 2. The code 312 is simply each letter's position, written in the same left-to-right order as the letters. Applying the same rule to BAD: B is 2, A is 1, D is 4, giving the code 214.

A Checklist of Common Coding Rule Types

Time-Pressure Strategy

1. Write the given word and its code directly above and below each other, letter by letter, so the transformation is visually obvious.
2. State the rule in one specific sentence before touching the new word at all.
3. Apply the rule letter by letter to the new word, writing out each intermediate step rather than trying to hold the whole transformation in your head.
4. Double check your final code against the rule one more time before selecting an option, since a single-letter slip changes the entire code.

Common Traps

• Assuming a constant shift after checking only the first letter of the pair, when the second or third letter reveals a different or inconsistent shift.
• Confusing a reverse-order rule with a position-swap rule, since both can look similar for short four-letter words.
• Forgetting that alphabet-position number codes must preserve the original left-to-right letter order, not sort the digits.
• Trying to match the new word directly against the answer options without deriving the rule first, which is slower and far more error-prone than deriving once and applying mechanically.

Building Speed Through Repetition

Coding and decoding items feel slow the first few times you practice them because writing out every letter-by-letter comparison seems tedious compared to just guessing. With repetition, though, the letter-to-position conversions from the letter series lesson and the shift-checking habit here become almost automatic, and most single-shift items drop to well under 20 seconds once the pattern is familiar. Treat your first pass through a set of coding practice items as deliberately slow and explicit - write every position number, every shift amount, every reversed letter - because that explicit repetition is what converts a 40-second item into a 15-second item by the time you sit the actual USTET. Rushing the practice phase to save time now almost always costs more time later, on test day, when a shaky shortcut fails under real pressure and you have no fallback method to recheck your work.