Count the 9s in the series below that have an even digit just before them and an odd digit just after them. How many such 9s are there?
8, 9, 6, 9, 2, 1, 5, 9, 7, 3, 1, 1, 9, 8, 8, 8, 2, 9, 9, 8, 9, 9, 9, 8, 2, 9, 1, 3, 6
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 3
Here a 9 is counted only when the digit just before it is even and the digit just after it is odd. Each 9 in the series is checked with its neighbours:
8, 9, 6 (2nd term): followed by 6, which is even, not counted
6, 9, 2 (4th term): followed by 2, which is even, not counted
5, 9, 7 (8th term): preceded by 5, which is odd, not counted
1, 9, 8 (13th term): preceded by 1, which is odd, not counted
2, 9, 9 (18th term): counted
9, 9, 8 (19th term): preceded by 9, which is odd, not counted
8, 9, 9 (21st term): counted
9, 9, 9 (22nd term): preceded by 9, which is odd, not counted
9, 9, 8 (23rd term): preceded by 9, which is odd, not counted
2, 9, 1 (26th term): counted
So the count is three (3).