Coding - Decoding
🔒 Log in to trackSubstitution and sentence coding
🔒 Log in to trackThe question gives things new names, like 'sky is called sea'. You work out the real-life answer first, then reply with its new name. A second format writes sentences in code words; a word shared by two sentences has the code they share.
What substitution means
The question gives things new names. You answer with the new name.
"If sky is called sea, where do birds fly?" Birds fly in the sky. The sky is called sea. So the answer is sea.
No calculation is needed. The only skill is keeping the real world and the renamed world apart.
The two-world method
- Answer the question in real life first. Where do birds fly? In the sky.
- Find the new name of that real thing in the chain. Sky is called sea.
- Give the new name as the answer: sea.
Rule: Use the real world for the fact. Use the renamed world for the answer.
Try one more. "If cold is called hot, what do we use to make ice?" Real answer: cold. Cold is called hot. So the answer is hot. The fact never changes. Only the name does.
Read each link in one direction
"Cloud is called rain" gives the new name of cloud only. It tells you nothing about the new name of rain. That comes from another link.
Take the chain: cloud is called rain, rain is called wind, wind is called sun. What do farmers wait for? Real answer: rain. Rain is called wind. So the answer is wind, not rain.
Watch: The real answer's word often appears in the chain as someone else's new name. Here "rain" is the new name of cloud. Picking "rain" is the trap.
Write long chains as a list
Long chains are easy to mix up. Write them as "real → new name":
- day → night
- night → morning
- morning → evening
When do we sleep? Real answer: night. And night → morning. So the answer is morning.
Word-code matching
Some questions write whole sentences in code words. 'red light' = 'pa ka' and 'green light' = 'ka na'.
The word 'light' is in both sentences. The code 'ka' is in both codes. So light = ka, and red = pa.
The full method is in the language coding lesson. In short:
- A word common to two sentences has the code common to them.
- Remove fixed codes. A leftover word takes the leftover code.
- If two codes still fit a word, its code cannot be determined.
Walk it once. 'hot tea' is 'na pi' and 'cold tea' is 'pi ka'. The word 'tea' sits in both sentences, and 'pi' sits in both codes, so tea = pi. The leftovers give hot = na and cold = ka. A third line, 'hot milk' = 'na ru', then fixes milk = ru.
Tip: Never match code words by position. The code order is usually jumbled.
Numbers standing for words
Some questions give a small dictionary: 1 = come, 2 = home, 3 = sweet, 4 = early. To code "come home early", write the numbers in the same word order: 1 2 4.
Decoding runs the dictionary the other way. The code '2 3' reads as home, then sweet: home sweet.
Question types you will see
Each type: how to recognise it, the method step by step, and one question to try.
Simple 'is called' chain
Lines like 'if pen is called pencil, pencil is called eraser …' end with an everyday question.
Answer the everyday question with the real thing.
Find the new name of that real thing in the chain.
Give the new name as the answer.
The chain only renames things; the fact is real, but the answer must use the new name.
If pen is called pencil, pencil is called eraser, eraser is called book and book is called bag, what do we use to write with ink?
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Real answer: we write with ink using a pen.
Pen is called pencil.
Pencil
Word-code matching by elimination
Two or three English sentences are given with code words, usually in jumbled order.
Find words common to two sentences; their code is the common code.
Fix those codes and remove them from each sentence.
A leftover word takes the leftover code.
A word's code must appear in every sentence that contains the word.
In a code language, 'hot tea' is 'na pi', 'cold tea' is 'pi ka' and 'hot milk' is 'na ru'. What is the code for 'milk'?
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'hot' is in sentences 1 and 3; 'na' is in both codes. So hot = na.
In 'hot milk' = 'na ru', milk takes the other code.
ru
Cannot be determined (two codes left)
The asked word appears in only one sentence, and two codes in that sentence are still unclaimed.
Fix every code you can with common words.
Count the codes still possible for the asked word.
If two remain, answer 'cannot be determined'. Never guess.
With jumbled codes, two leftover codes are equally possible until something pins one down.
In a code language, 'good boy' is 'mi ra' and 'good girl smiles' is 'ra su to'. What is the code for 'girl'?
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'good' is common and 'ra' is common, so good = ra.
In the second sentence, 'girl' and 'smiles' share 'su' and 'to'.
Nothing tells them apart.
Cannot be determined
Long chains
A chain of four or five renames, often with the real answer hidden in the middle.
Write the chain as a list: real → new name.
Answer the question in real life.
Walk from that real thing to its new name.
A written list stops you from mixing up the two worlds.
If train is called bus, bus is called ship, ship is called aeroplane, aeroplane is called rocket and rocket is called car, what flies in the sky carrying passengers?
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Real answer: an aeroplane.
In the list, aeroplane → rocket.
Rocket
A small dictionary of numbers and words
A short list like '1 means pen, 2 means book' is given. The code of a phrase, or the meaning of a number pair, is asked.
Read the dictionary once and write it as word → number.
For a phrase, replace each word by its number.
Keep the phrase's own word order.
For decoding, read the numbers back as words.
The dictionary fixes every word, so only the order needs care.
In a certain code, 1 means pen, 2 means book, 3 means bag and 4 means chair. How is 'chair pen' written in this code?
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chair → 4 and pen → 1.
Write the numbers in the phrase's order.
4 1
Shortcuts that save time
Write each sentence above its code. Tick the words that repeat and the code words that repeat. The word you need is either matched directly or is the one item left over.
'red light' = 'pa ka' and 'green light' = 'ka na'. What is the code for 'red'?
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'light' is in both sentences and 'ka' is in both codes, so light = ka.
In the first sentence, red takes the other code.
pa
Mistakes to avoid
Where most students lose marks on this subtopic.
Answering with the real-world word ('rain') instead of its new name.
Find the real answer, then look up what it is called.
Reading a link backwards ('cloud is called rain' taken as the new name of rain).
A link names only the word on its left.
Matching code words by their position in the sentence.
Match by common words and common codes. The order is jumbled.
Picking one of two possible codes.
If two codes still fit, the answer is 'cannot be determined'.
Missing a repeated word written as a plural (light and lights).
Treat them as different words unless the question says otherwise.
Quick revision
Read this the night before the exam.
Real answer first, then its new name.
Each link names only the word on its left.
Write long chains as a list: real → new name.
Sentence codes: common word ↔ common code; then remove fixed codes.
Two codes still possible → cannot be determined.
Codes for a phrase follow the phrase's own word order.
Practice: 13 questions
Sets of 10, mixed across the question types above. Every answer has a step-by-step explanation.
Topic test · 13 questions
Suggested time 8 min · wrong answers go to your mistake notebook automatically.