Q. In the series AABABCABCDABCDE.., which letter appears at the 100th place?
a. G
b. H
c. I
d. J
Correct Answer: c. I
Question from UPSC Prelims 2022 CSAT Paper
Explanation :
In the series aababcabcdabcde , 100th letter ?
Given Series = A (1 Letter) AB (2 Letters) ABC (3 Letters) ABCD (4 Letters) ABCDE (5 Letters) …… so on up to 100th letter.
Sum of first 13 natural numbers = 1 + 2 + 3 + 4 + 5 ….. 13 = n(n+1)/2 = 13×14/2 = 91.
So, if we have to count upto 100th letter, in the last string (100 – 91) = 9 letters would be there.
Which would be – ABCDEFGHI.
So I is the correct answer.
