What is Code Numbers?
Code number questions work like code words, but instead of letters being replaced by other letters, numbers are encoded using a system you need to figure out. You might be given coded sums or number-word pairs.
These questions test logical thinking and pattern recognition. They require careful, methodical working to avoid small errors that lead to wrong answers.
Step-by-Step Method
Read all the coded pairs
Look at every given pair of numbers and their codes. Write them out neatly.
Compare to find patterns
Look for digits that appear in multiple numbers. Check if they always map to the same code.
Build your code key
Create a list matching each digit (0-9) to its coded value as you discover them.
Decode and verify
Apply your code key to the target number. Double-check by encoding your answer back to see if it matches.
Worked Examples
If 347 is coded as PQR and 731 is coded as RPE, what is the code for 143?
Working
- From 347 = PQR: 3=P, 4=Q, 7=R
- From 731 = RPE: 7=R, 3=P, 1=E
- 3=P and 7=R confirmed in both.
- 143: 1=E, 4=Q, 3=P
If 256 is coded as FGH and 562 is coded as HGF, what does GHF stand for?
Working
- From 256 = FGH: 2=F, 5=G, 6=H
- From 562 = HGF: 5=H… but 5=G from the first. Conflict.
- Re-examine: 562 = HGF means position-wise 5=H, 6=G, 2=F. But from 256: 5=G, 6=H.
- This means the codes are consistent by position only if we recheck. 256=FGH and 562=HGF. Notice 2=F in both cases. 5=G and 6=H from first; 5=H and 6=G from second – the code is reversed!
- GHF would decode as: G=5, H=6, F=2
Common Mistakes
Rushing and mixing up which digit maps to which code letter.
Write each mapping on a separate line and verify it against every given pair before moving on.
Assuming the code follows a mathematical pattern (like adding 1 to each digit).
Codes are arbitrary mappings – always derive them from the given pairs, never assume a formula.
Top Tips
- Treat each digit independently, just like code words treat each letter independently.
- Look for digits that appear in multiple given numbers – they help you confirm your mappings.
- Write your code key clearly: 0=?, 1=?, 2=?, etc.
- Check your final answer makes sense before moving on.
Ready to practise?
Put these techniques into action with our free practice papers.
Practise Verbal Reasoning Questions