First, notice that the names of each month correspond to the number of the month in the calendar. For example:
January - 1월
February - 2월
December - 12월When counting months, you can either use 달 or 개월. When using 달, you must use the pure Korean numbers, and when using 개월, you must use the Sino-Korean numbers. There is no difference in meaning, and both are used frequently. When putting a number before 달, I prefer to write the Korean word. When putting a number before 개월, it doesn't matter if you use the word or the numeral.
저는 두 달 동안 한국어 수업을 들었어요 - I took a Korean class for 2 months
저는 2개월 동안 한국어 수업을 들었어요 - I took a Korean class for 2 months
저는 이 개월 동안 한국어 수업을 들었어요 - I took a Korean class for 2 monthsSomeone told me that '동안' is actually incorporated into the meaning of 달, which would mean that you wouldn't have to say 동안 after 달. Still, though, most people use 동안 after 달.

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LEARN KOREAN (한국어) [GRAMMAR] #1
RandomThis is book #1 for the Korean Language series. Try to understand all of the notes in this book before you proceed to the next one. Good luck ! This book contains Korean grammar. Try to understand it so that you can understand how to make a sentence...