Count the 5s in the series below that have an even digit just before them and an odd digit just after them. How many such 5s are there?
6, 5, 3, 2, 5, 8, 4, 5, 7, 9, 5, 1, 8, 5, 9, 2, 5, 5, 3, 4, 5, 1, 7, 5, 6, 2, 5, 9, 4
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 6
Here a 5 is counted only when the digit just before it is even and the digit just after it is odd. Each 5 in the series is checked with its neighbours:
6, 5, 3 (2nd term): counted
2, 5, 8 (5th term): followed by 8, which is even, not counted
4, 5, 7 (8th term): counted
9, 5, 1 (11th term): preceded by 9, which is odd, not counted
8, 5, 9 (14th term): counted
2, 5, 5 (17th term): counted
5, 5, 3 (18th term): preceded by 5, which is odd, not counted
4, 5, 1 (21st term): counted
7, 5, 6 (24th term): preceded by 7, which is odd, not counted
2, 5, 9 (27th term): counted
So the count is six (6).