The general rule is that native Korean numbers are used for small numbers and Sino-Korean are used for large numbers with 명. There is no specific standard for the small numbers and large numbers. If the numbers are over 100, Sino-Korean numbers are used mostly. If the numbers are below 19, native Korean numbers are used mostly. If the numbers are between 20 and 99, both Sino-Korean numbers and native Korean numbers are used. But Sino-Korean numbers are more commonly used nowadays.