how to say "it's not that" in Korean I mean like a sentence like "it's not that I don't like you" you're saying the reason you're doing something is not what people might assume such as 1. your friend failed an exam and you say to another friend "it's not that he's stupid, it's just that he hates studying" 2. Somebody thinks you can't speak English. You know how to, you're just too shy to talk. "it's not that I can't speak English. I'm just shy" 3. Coworker always eat vegetables for lunch and you think she must like vegetables. But she says "It's not that I like vegetables. They're just good for health" 4. You're a manager scolding an employee and you say "It's not that I like being mean. I just have to be firm with staff" weird sentences I know. translations and grammar explanations would be helpful I think I saw that these sentences would use this grammar pattern "는게 아니다" or something

How to say "I'm not as stupid as I look" in Korean?

Lol this is a weird sentence, I know. But I was curious. I want to say it jokingly to my Korean friends. But still politely.

I was also curious about other similar sentences "I'm not as (adjective) as"

Here are some random examples that I would like to know how to say in Korean

"I can't do it as well as my classmates can"
"I'm not as pretty as you"
"She's not as innocent as she seems"
"I'm not as weird as I appear to be"

How to say "some of" and "most of" in Korean?

I couldn't find a clear answer online, so I'm asking here :)

I'm not sure how to explain, but I want to use "some" like this

"Some of my classmates are crazy"
"I only know some words in this sentence" (as in I can't understand 100%)
"Most of my classmates are older than me"
"Most of her coworkers are rude"
"Some of them (people) are really friendly"
"He lived there for most of his life"

Translations of those would be good :-) thanks 

Differences between (으)니까, 서 According to my notes, you can use them similarly sometimes. I kinda get how to use them, but need more clarification. Could anyone give me some examples... like translate my sentences? Please. I think these random examples would help me differentiate because I want to say things similar to them. Sorry if they're weird and specific. If there are other grammatical structures other than 으니까 and 서 that would work better in the sentences below, please use those, but tell me why. "I'm learning Korean because I work with Korean people." "I can't go out this weekend because I'll be too busy" "The movie was boring, so I turned off the TV" "I can't buy this shirt because I don't have enough money for it" "I'm not good at A, so I don't like doing A" ( I couldn't think of an example ) "I'm tired, so let's just get out of here" "You look better with short hair, so you should get a haircut" "It's cold outside, so let's go out when it's warmer." "Since you're not listening, I'll stop talking"