CSAT 2022

Q. What is the value of X in the sequence 2, 12, 36, 80, 150, X?

a. 248
b. 252
c. 258
d. 262
Correct Answer: b. 252

Question from UPSC Prelims 2022 CSAT Paper

Explanation : 
2, 12, 36, 80, 150, X

Consider the differences between consecutive terms:

12 – 2 = 10
36 – 12 = 24
80 – 36 = 44
150 – 80 = 70

Now let’s examine the differences between these differences:

24 – 10 = 14
44 – 24 = 20
70 – 44 = 26

We see that the differences between the differences are increasing by 6 each time. Therefore, to find the next difference between consecutive terms, we can add 6 to the last difference between differences:

26 + 6 = 32

Now we can add this difference to the last difference between consecutive terms in the original sequence:

70 + 32 = 102

Finally, to find the value of X, we can add this difference to the last term in the original sequence:

150 + 102 = 252

Thus, the value of X is 252 (option b).

More Questions:
UPSC Factory for Windows
Get Syllabus Tracker, Prelims PYQs (3000+), Mains Model Answers, NCERT Books, Topper Notes & Answer Sheet, Strategy, Past Paper for Offline Study. Click to Install !!
UPSC Factory App
Get everything you need for upsc preparation with just one click! Install now!