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Refer to the given series and answer the question that follows (all numbers are single-digit numbers only, and all counting is to be done from left to right).
How many such odd digits are there, each of which is immediately preceded by an even digit and also immediately followed by an odd digit?
5
0
4
3
4
Identify triplets in the pattern (Even - Odd - Odd) by scanning the series. The middle 'Odd' digit is the one preceded by an even digit and followed by an odd digit.
Identify triplets in the pattern (Even - Odd - Odd) by scanning the series. The middle 'Odd' digit is the one preceded by an even digit and followed by an odd digit.
Define the target condition
We are looking for three consecutive digits forming the triplet (Even digit, Odd digit, Odd digit). The question asks for an odd digit preceded by an even digit and followed by an odd digit.
Scan the series for triplets
Let's check segments: (4,4,9) X, (4,9,6) X, (6,8,1) X, (8,1,3) O, (1,3,9) O (if we consider overlapping triplets: 8,1,3 and 1,3,9... Wait, let's process carefully: [8,1,3] Yes, [4,3,9] Yes, [8,5,7] Yes, [8,9,5] Yes).
Verify each match
1: (8,1,3) тЖТ Even(8), Odd(1), Odd(3) [Matches]; 2: (4,3,9) тЖТ Even(4), Odd(3), Odd(9) [Matches]; 3: (8,5,7) тЖТ Even(8), Odd(5), Odd(7) [Matches]; 4: (8,9,5) тЖТ Even(8), Odd(9), Odd(5) [Matches]. Total count = 4.
A: 2 is incorrect. B: 3 is incorrect. D: 5 is incorrect. The count of such patterns is exactly 4 based on the verified sequence scan.
C is correct because there are exactly 4 instances (8-1-3, 4-3-9, 8-5-7, 8-9-5) where an odd digit is preceded by an even digit and followed by an odd digit.
When counting specific patterns in long sequences, always write down the series and mark the matches to avoid missing overlapping sequences or miscounting.
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