The binary number system (base 2) uses only two digits, 0 and 1. Each digit's place value is a power of 2, starting from 2⁰ for the rightmost digit, then 2¹, 2², and so on, moving left. To convert a binary number to decimal, multiply each digit by its corresponding power of 2 and sum the results. For 111 in binary: The rightmost digit (1) is at the 2⁰ place. The middle digit (1) is at the 2¹ place. The leftmost digit (1) is at the 2² place. Decimal value = (1 × 2²) + (1 × 2¹) + (1 × 2⁰) = (1 × 4) + (1 × 2) + (1 × 1) = 4 + 2 + 1 = 7.