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).