CSAT 2021

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 : 

This is a question about finding the pattern in a sequence of numbers. The given sequence is 2, 7, 22, 67, 202, X, 1822. To find the value of X, we need to determine the pattern that generates the sequence.

If we look at how each number in the sequence is generated from the previous one, we can see that each number is obtained by multiplying the previous number by 3 and then adding 1. For example:

To get from 2 to 7: (2 * 3) +1 = 7
To get from 7 to 22: (7 *3) +1 =22
To get from 22 to 67: (22 *3) +1 =67
To get from 67 to 202: (67 *3) +1 =202
Using this pattern we can find that X should be equal to (202*3)+1=607.

Therefore the correct answer is c) 607.

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