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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 even digits are there each of which is immediately preceded by a perfect square and immediately followed by an odd digit? (Note: 1 will be considered as a perfect square.)
0
2
3
4
2
Scan for even numbers, then check if the digit to the left is a perfect square (1, 4, 9) and the digit to the right is odd.
Scan for even numbers, then check if the digit to the left is a perfect square (1, 4, 9) and the digit to the right is odd.
Identify criteria and list numbers
The series is: 3, 5, 5, 7, 1, 6, 1, 8, 8, 7, 6, 2, 2, 5, 9, 8, 1, 1, 5, 3, 3, 2, 8, 1, 7, 9, 2. Criteria: (Perfect Square) (Even) (Odd).
Evaluate triplets
Perfect squares are 1, 4, 9. Checking triplets: (1,6,1) тЖТ 6 is even, 1 is sq, 1 is odd (Yes). (1,8,7) тЖТ 8 is even, 1 is sq, 7 is odd (Yes). (9,8,1) тЖТ 8 is even, 9 is sq, 1 is odd (Yes). (1,2,5) тЖТ 2 is even, 1 is sq, 5 is odd (Yes). (1,2,8) тЖТ No. (9,2,end) тЖТ No.
Final count verification
The valid triplets are: 1,6,1; 1,8,7; 9,8,1; 1,2,5. Total count is 4.
A: Represents an incorrect count. C: Represents an incorrect count. D: Represents an incorrect count.
B is correct because there are exactly 4 instances where an even digit is preceded by a perfect square (1 or 9) and followed by an odd digit.
When counting patterns, write out the series and physically underline or group the qualifying sets to avoid skipping elements.
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