5217381965421965894321786 In the above series, how many 1s are preceded by 2 and immediately followed by 7?
A
3
B
4
C
1
D
2
Correct Option:
D
Explanation
We must count every 1 that is immediately preceded by 2 and immediately followed by 7—in other words, occurrences of 217. The given number string contains 217 twice, so the answer is 2.
