In the sequence 1, 5, 7, 3, 5, 7, 4, 3, 5, 7, how many such 5s are there which are not immediately preceded by 3 but are immediately followed by 7?

Correct Answer: (A) 1

In the sequence 1, 5, 7, 3, 5, 7, 4, 3, 5, 7, we inspect each occurrence of 5 for being not preceded by 3 and followed by 7: the first 5 (in 1, 5, 7) is preceded by 1 and followed by 7 (valid); the second 5 (in 3, 5, 7) is preceded by 3 (invalid); the third 5 (in 3, 5, 7) is also preceded by 3 (invalid). Thus, there is exactly 1 valid occurrence.