Difficulty: Easy
Correct Answer: 1101
Explanation:
Introduction / Context:
BCD encodes each decimal digit (0–9) as a 4-bit binary value. Recognizing valid versus invalid 4-bit patterns is essential for input validation, display drivers, and error checking in digital systems that use BCD instead of pure binary.
Given Data / Assumptions:
Concept / Approach:
Check whether the given 4-bit code is less than or equal to 1001. If it exceeds 1001, it cannot represent a decimal digit in BCD and is therefore invalid.
Step-by-Step Solution:
Verification / Alternative check:
List all invalid BCD codes: 1010, 1011, 1100, 1101, 1110, 1111. 1101 is in this set.
Why Other Options Are Wrong:
Common Pitfalls:
Confusing BCD with hexadecimal, where 1010–1111 would be valid (A–F). In BCD, those patterns are illegal for single digits.
Final Answer:
1101
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