Find the next number: 2, 6, 12, 20, 30, ?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of Aptitude & Reasoning conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
Look at the differences: 4, 6, 8, 10, which increase by 2 each time. The next difference is 12, so the next term is 30 + 12 = 42.
Alternative view: the terms are n(n+1) for n = 1, 2, 3, 4, 5, 6 -> 2, 6, 12, 20, 30, 42.
Both patterns are valid; identifying either leads to 42. When solving number series always check first and second differences, ratios and known formulas.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.