How many books are there?

There are two numbering system in Korean: Korean numbers
and Sino-numbers. Korean numbers are used mostly for counting, while Sino-Korean numbers are used with words that originated from the Chinese language.
when counting(things+개, people+명, bottles+병, books+ 권 pieces of paper+장, animals+마리, flowers+송이).
개, 명, 병, 권 we are called them counters. Note that when used with counters, the following Korean numbers change the forms: 하나-> 한 개, 둘-> 두 개, 셋->세 개, 넷-> 네 개.