It is a characteristic of korean language in vocabulary.
There are many words originated from chinese in korean and
we use two different type words because of a strong point of chinese alphabet.
As you know , each chinese letter has it's own meaning, so we can
describe something briefly .
For example, '일,이,삼,사,오,육,칠,팔,구,십(一二三四五六七八九十)'
is more simple than
especially,when we calculate or memorize big number , the former is faster and more advantageous.