What is the value of ‘X’ in the sequence 2, 7, 22, 67, 202, X, 1822?
Answer & explanation
Answer: (c) 607
Every term is three times the previous one plus 1. So X = 202 × 3 + 1 = 607, and 607 × 3 + 1 = 1822 confirms it.
- 2 × 3 + 1 = 7, 7 × 3 + 1 = 22, 22 × 3 + 1 = 67, 67 × 3 + 1 = 202 — each term is 3 × previous + 1.
- X = 202 × 3 + 1 = 607.
- Check: 607 × 3 + 1 = 1822, the next term.
Remember · When terms roughly triple, test '× 3 ± k', and always verify with the term after the blank.
Question and answer: UPSC's official GS Paper II (2021, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·