Coding and Decoding Notes & Questions | Class 5 Reasoning | Drishti OS

Coding and Decoding

How simple letter-shift codes work (each letter moves forward or backward a fixed number of places).
How to decode a word once you know the rule used to make the code.
How letters can be turned into numbers (A=1, B=2, ... Z=26) to build number-based codes.

Verbal: Every letter of the word moves forward by the same number of places in the alphabet.

Symbolic: If CAT is coded as DBU, each letter moved forward by 1 (C->D, A->B, T->U).

Word	Shift	Code
DOG	+2	FQI
SUN	+1	TVO

Verbal: First reverse the order of the letters, then shift each letter forward.

Verbal: Replace each letter with its alphabet position (A=1 ... Z=26) and add the numbers together.

Example: CAT -> C=3, A=1, T=20 -> sum = 24.

If BAT is coded as CBU (shift +1), how is CAT coded?

Step 1 - Rule: shift each letter forward by 1
Step 2 - C -> D, A -> B, T -> U
Answer: DBU

If each letter's number is added up, what is the code for DOG?

Step 1 - D=4, O=15, G=7
Step 2 - Sum = 4 + 15 + 7 = 26
Answer: 26

Mistake	Why it happens	Fix
Shifting the wrong direction	Confusing forward and backward	Check the example pair carefully first
Forgetting to reverse before shifting	Skipping a step	Write the reversed word first, then shift
Wrong alphabet number	Miscounting from A	Use a written A-Z=1-26 chart
Adding numbers incorrectly	Arithmetic slip	Add the numbers one at a time, checking the running total

If letters shift forward by 2, what does BUS become?
What is the alphabet number of the letter M?
Reverse the word MAP.
Stretch: If CAT is coded using letter-number sum, and DOG uses the same rule, which word has the bigger code?

Revision tip: Always confirm the rule using the example pair before decoding the new word.

Open the Practice tab for graded questions on Coding and Decoding.