Both are correct. But the point is: 1. In the native Korean numbers, - It is actually from 1 to 99, and it doesn't have three and more digit units like "hundred", "thousand", etc. - So, it partially uses Sino Korean numbers for the three and more digit units only. And for one and two digit numbers, it still uses its own native numbers. - So if it is 205, 200 is using Sino Korean, but 5 is still using native number. - If it is 5245, 5000 and 200 are using Sino Korean, and 40 and 5 are using native Korean. 2. The main difference between the native and Sino is: 1) Native is for "counting" numbers, like for "how many", while Sino is for both "counting" and "calling" the numbers. Calling the number is to say "Room number", "Address", "Telephone numbers", etc. So, if you "call" the number 205 as in "Room number 205", you use Sino like 이백오. But if you "count" the number 205 as in - "I did it 205 times", then you can use both Sino or Native like "이백오번 했어" or "이백 다섯번" 했어. - "I have 205 apples": 나 사과 이백오개 있어 or 나 사과 이백다섯개 있어. 2) Normally the native Korean number is for counting "small numbers". That is why for time, the hour uses the native Korean because it is only up to 12, and minutes and seconds use Sino, because 60 is bigger. But there's no the definition of "small number", and it varies depending on each person or situations. Normally, if the number is over 40, 50, and more, it is getting complicated even to native Koreans, so maybe if kids count some numbers, they will start from the native, and will probably convert it into Sino at some point like over 40, 50, 60, etc. So, 205 is big or small? The three digit number 200 is using Sino, so you can put it aside. So, it is just 5. I can say it is small enough, so I might use the native numbers or Sino numbers. But if the number is 287, then the two digit number is 87 which is quite big among the numbers from 1 to 99. Then, I don’t think I would use the native when I’m counting that number.