Hello Native korean number system is used when talking about Age, number of people, hour of the day, number of hours, number of things.. The sino korean number system is used when talking about Age, date, temperature, measurements (i.e. miles), minutes and secodns, phone numbers, money... The good thing would be ti try and find some videos on youtube that use numbers to see the difference Hope this helps^^ btw after 100, you could say that there is only just one number system so it makes it a little bit more easier