1. 시험을 봤는데 한 시간 쯤 걸렸어요 가: 우와, 한 시간이나 걸렸어요? => surprised at how long it took. (he did it slow) 나: 에이, 한 시간밖에 안 걸렸어요? => underwhelmed at how little time it took. (he did it fast) -이나 expresses "as much as ...", i.e, a great magnitude. -밖에 안... is the opposite; "as little as", "no more than", "only". The exclamation 우와 indicates a surprise or awe, 에이 a disappointment or scorn. ("우와" is also shortened to "와", which happens to sound like English "wow!".) - 우와, 이자가 백만원이나 붙었네: Wow, it accrued as much as a million won in interest. - 에이, 이자가 오만 원밖에 안 붙었네: Gee, it accrued only fifty thousand in interest. 2. 숙제를 했는데 다섯 개 틀렸어요 가: 우와, 대섯 개나 틀렸어요? => Wow, have I got as many as five wrong? * This is strange because people don't express a pleasant surprise at bad results. 나: 에이, 대섯 개밖에 안 틀렸어요? => Gee, have you only got five wrong? * Another strange sentence. Why disappointed if he got so few wrong? * 우와 and 에이 should be swapped for them to make sense. * In Korean generally 우와 is used for a good surprise, and 이에 for bad one. English's "wow" and "gee" are not so clear cut, I think. 3. How should I answer if my question is already negetive? * If the Q and A agrees (neg A to neg Q, or pos A to pos Q), you say 예. * If not, you say 아니요. It is sort of opposite to English for negative questions. 오늘 안 온 사람이 많아요? => 예, 안 온 사람이 많아요. => 아니요, 안 온 사람이 별로 없어요. 오늘 날씨가 춥지 않죠? It's not cold today, isn't it? => 예, 춥지 않아요. No, it is not cold. (예 and No not in agreement) => 아니요, 추워요. Yes, it is cold. (same) As mentioned, the sentences of #1 and #2 are a little strange. In #1, how long the exam took is generally not something you are awed or disappointed about. So it's a bit odd. #2, looks completely wrong to me. We express disappointment if "다섯개나" is wrong, which means "as much as five, not "우와".