Counting subtraction input combinations For one-bit binary subtraction without borrow-in, how many distinct input combinations (A,B) exist?

Introduction / Context:
Designing a one-bit subtractor begins with enumerating all input combinations. This ensures complete coverage for truth-table-based or Boolean design.

Given Data / Assumptions:

• Inputs A and B are single bits.
• No borrow-in.

Concept / Approach:
Two binary inputs yield 2^2 = 4 distinct combinations. Each combination defines the resulting difference and borrow-out.

Step-by-Step Solution:
Compute total combinations: 2 inputs → 2^2 = 4.Enumerate: (0,0), (0,1), (1,0), (1,1).Hence, there are four basic combinations.

Verification / Alternative check:
Cross-check with a subtractor truth table; it contains four rows for A,B without borrow-in.

Why Other Options Are Wrong:
3, 2, 1: do not account for all A,B permutations.

Common Pitfalls:
Confusing “operations” with “results” or mixing in borrow-in, which doubles the rows.

Final Answer:
4