Convert 496 to Roman numerals and 23 to binary, and add two binary numbers.

400 is represented as CD (500 - 100).
90 is represented as XC (100 - 10).
6 is represented as VI (5 + 1).

The Roman numeral is $\boxed{\text{CDXCVI}}$.

13. Convert $23_{\text{ten}}$ to binary.

15. Add: $101_{\text{two}} + 11_{\text{two}}$

$1_{\text{two}} + 1_{\text{two}} = 10_{\text{two}}$. Write down 0, carry over 1.

$0_{\text{two}} + 1_{\text{two}} + 1_{\text{carry}} = 10_{\text{two}}$. Write down 0, carry over 1.

$1_{\text{two}} + 0_{\text{two}} + 1_{\text{carry}} = 10_{\text{two}}$. Write down 10.

The sum is $\boxed{1000_{\text{two}}}$.