1. The problem is to simplify the expression $1101_2$ which is a binary number. 2. To simplify or understand a binary number, we convert it to decimal (base 10). 3. The binary number $1101_2$ means: $$1 \times 2^3 + 1 \times 2^2 + 0 \times 2^1 + 1 \times 2^0$$ 4. Calculate each term: $$1 \times 8 + 1 \times 4 + 0 \times 2 + 1 \times 1 = 8 + 4 + 0 + 1$$ 5. Add the values: $$8 + 4 + 1 = 13$$ 6. Therefore, the binary number $1101_2$ simplifies to the decimal number $13$.