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Question

What is the BCD code for decimal digit 3?

This question was previously asked in
RRB JE 2025 CBT 2 Mechanical and Allied Engg Question Paper English (2-Jul-2026) (Shift-1)
The correct answer is

0011

This question tests BCD (Binary Coded Decimal) encoding. In BCD, each individual decimal digit from 0 to 9 is represented by its own 4-bit binary group using the standard 8-4-2-1 positional weights. Because a 4-bit field can hold values 0–15 but only 0–9 are valid decimal digits, the six combinations 1010 through 1111 are invalid/unused in BCD.

To find the code for decimal 3, convert 3 to 4-bit binary using the place values 8, 4, 2, 1:

  • 8 → 0, 4 → 0, 2 → 1, 1 → 1
  • 3 = 2 + 1 = 21 + 20 = 0011

So the BCD code for decimal 3 is 0011, the correct answer. A short reference:

DecimalBCD
10001
20010
30011
50101
60110

Why the other options are wrong:

  • 0001 is the code for decimal 1 (weight 1 only).
  • 0101 equals 4 + 1 = 5, so it is the code for decimal 5.
  • 0110 equals 4 + 2 = 6, so it is the code for decimal 6.
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Important Questions from Binary Codes

  1. Which of the following is/are the popular techniques for error detection?

  2. What is maximum number represented by 4 bit BCD code?
  3. A code in which each decimal digit is represented by a group of 4 binary bits is

  4. What would be the gray code equal to the number 14?

  5. BCD equivalent of (345)10 is:

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