Q. What is the value of ‘X’ in the sequence 2, 7, 22, 67, 202, X, 1822?
(a) 603
(b) 605
(c) 607
(d) 608
Correct Answer: (c) 607
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
Given sequence: 2, 7, 22, 67, 202, X, 1822
Pattern: Each number is generated by multiplying the previous number by 3 and adding 1.
Let’s verify each step:
2 → 7: 2 × 3 + 1 = 7
7 → 22: 7 × 3 + 1 = 22
22 → 67: 22 × 3 + 1 = 67
67 → 202: 67 × 3 + 1 = 202
202 → X: 202 × 3 + 1 = 607
607 → 1822: 607 × 3 + 1 = 1822
Answer: X = 607