Coding-decoding hides a simple rule inside a word. Find the rule, and the answer follows.
This lesson covers the alphabet table and five common coding types with solved examples and traps.
- Table: A is 1, Z is 26.
- Shift: Move letters along.
- Opposite: A with Z.
- Numbers: Use positions.
- Words: Match common parts.
What Is Coding-Decoding?
What does the question ask?
A word is changed into a code using a secret rule. You see one example of the rule.
Then you must code a new word, or decode a given code, using the same rule.
Why is it easy to score?
The rule is always simple. It only hides in plain sight.
Once you spot the rule, the rest is quick work.
Check
Coding-decoding questions use a hidden rule.
First Tool: The Alphabet Table
What should you memorise?
A is 1, B is 2, and so on up to Z, which is 26.
Learn a few anchors: E is 5, J is 10, O is 15, T is 20 and Y is 25.
What is the opposite letter trick?
The first letter pairs with the last: A with Z, B with Y, C with X.
Any two opposite letters have positions that add up to 27.
Check
A and Z are opposite letters.
Type One: Letter Shifts
What is a fixed shift?
Every letter moves forward or backward by the same number of places.
Take RAIN coded as SBJO. Each letter moved forward by 1.
Can you see another one solved?
Suppose MOON is coded by moving each letter forward 2 places.
M becomes O, O becomes Q, O becomes Q and N becomes P. The code is OQQP.
Why this works: the same step is applied to every letter, so one example reveals the rule for the whole word.
How do you spot the shift from an example?
Take FISH coded as GJTI. Compare F and G, I and J, S and T, H and I.
Each pair is one place apart, so the rule is +1 on every letter.
Why this works: if one pair gives +1, check the other pairs. All must match.
What about a changing shift?
The shift can grow: +1, +2, +3 for the first, second and third letters.
Under that rule, CAT becomes DCW.
Step by step: C + 1 = D, A + 2 = C and T + 3 = W.
Why this works: the shift itself follows a pattern, so name the pattern first.
Check
A fixed shift moves each letter by the same number of places.
Type Two: Opposite Letters
How does this code work?
Each letter is replaced by its opposite in the alphabet.
B becomes Y, O becomes L and Y becomes B.
Can you see one solved?
Code BOY using opposite letters. Swap each letter for its mirror partner.
So BOY is written as YLB.
Why this works: B is 2 and 27 – 2 = 25, which is Y. Use 27 – n for any letter.
Check
Under the opposite-letter rule, A becomes B.
Type Three: Number Codes
How do numbers enter?
A word may be coded as its letter positions, or as their sum.
Always test both ideas on the example first.
Can you see one solved?
Take BAD. The positions are 2, 1 and 4. Their sum is 7.
If CAB is coded as the positions in order, it becomes 312.
Can you try a harder number code?
Suppose DOG is coded as 4157. Its positions are 4, 15 and 7.
So the code simply writes the three positions in order, joined together.
Now code BAG: B is 2, A is 1 and G is 7, so the code is 217.
Why this works: write the positions under the example first, then copy the same plan.
What about a word length code?
Some codes just count something, like the number of letters.
Check the example before you trust a guess.
Check
A number code can use the sum of letter positions.
Type Four: Rearranging Letters
What does rearranging look like?
Letters stay the same but change order. A word may be reversed, or its first letter moves to the end.
Take LIGHT becoming IGHTL. The first letter moved to the back.
Step by step: L moves to the end, leaving IGHT, then L. So LIGHT becomes IGHTL.
Why this works: compare the example with the original, letter by letter, and note where each letter went.
Is sorting a rearrangement?
Yes. Some codes sort the letters in alphabetical order.
Compare the example letter by letter to see which one it is.
Check
A rearranging code keeps the same letters.
Type Five: Word-to-Word Codes
What are these questions?
You get coded sentences. Each word has a code word.
Find a word that appears in two sentences. Its code word must appear in both codes.
Can you see one solved?
Suppose red car is ab cd, and blue car is ef cd.
The common word car matches the common code cd. So red is ab.
Now find blue: the second code ef cd has cd for car, so blue is ef.
Why this works: a word that repeats must have a code word that repeats.
Check
A word shared by two sentences shares a code word.
Common Traps and Quick Tips
What mistakes cost marks?
Trying only one rule. If the first rule fails on one letter, test another.
Forgetting to check the rule on every letter of the example.
How do you stay quick?
Write the letter positions under the example word. The pattern often shows at once.
Test your rule on the whole example before using it on the new word.
How should you practise?
Solve five coded words a day and name the rule each time.
Then try the quiz below and read every explanation.
Check
One matching letter proves the rule.
Exam Traps
Write letter positions under the example.
Test a fixed shift first.
Try the opposite-letter rule next.
Check number codes for sums.
Test the rule on every letter.
MCQ on Coding-Decoding
0 of 1 answered Question 1 of 1 0 of 1 answered Question 1 of 1 0 of 1 answered Question 1 of 1 0 of 1 answered Question 1 of 1 0 of 1 answered Question 1 of 1 0 of 1 answered Question 1 of 1 0 of 1 answered Question 1 of 1
Leave a Reply