A smaller numeric code — Coding & Decoding Aptitude Question
A smaller numeric code: If 2 = 6, 3 = 12 and 4 = 20, then 5 = ? Answer and worked solution on CodeKairo.
- Topic: Coding & Decoding
- Section: Logical Reasoning
- Difficulty: Easy
- Time target: 60 seconds
Question
If 2 = 6, 3 = 12 and 4 = 20, then 5 = ?
Options
- 25
- 28
- 30
- 36
Show the answer and the worked solution
Correct answer: C. 30
Worked solution
- The rule is n × (n + 1).
- 5 → 5 × 6 = 30.
Answer: 30.
The idea
The same rule in smaller numbers. Recognising n(n + 1) — the doubled triangular numbers — makes these instant.
Shortcut. The outputs 6, 12, 20 rise by 6 and then 8, so the next rise is 10: 20 + 10 = 30.
Common trap. "25" — squaring 5 by reflex; the examples rule that out immediately, since 2 maps to 6, not 4.