How many such 5's are there in the following number sequence, each of which is immediately preceded by 3 or 4 but not immediately followed by 8 or 9?
3 5 9 5 4 5 5 3 5 8 4 5 6 7 3 5 7 5 5 4 5 2 3 5 1 0
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Five
We examine each 5 in the sequence and apply the conditions:
Condition:
- Immediately preceded by 3 or 4, and
- Not immediately followed by 8 or 9
Sequence:
3 5 9 5 4 5 5 3 5 8 4 5 6 7 3 5 7 5 5 4 5 2 3 5 1 0
Valid 5’s:
- 4 5 5 → preceded by 4, followed by 5
- 4 5 6 → preceded by 4, followed by 6
- 3 5 7 → preceded by 3, followed by 7
- 4 5 2 → preceded by 4, followed by 2
- 3 5 1 → preceded by 3, followed by 1
Invalid cases:
- 3 5 9 → followed by 9
- 3 5 8 → followed by 8
- Other 5’s not preceded by 3 or 4
Total valid 5’s = 5