1. The subways in Seoul are clean, safe, and fast.
1-2. The subway in Seoul is clean, safe, and fast.
(Are both OK?)
2. He is different from Tom in character.
2-1. He is the same as Tom in character.
2-2. His character is different from Tom's.
(Are the sentences grammatical? Which one do I have to use?)
3. Visitors can find subway maps in all the stations and on the trains.
(Do I have to use the term 'train' in the subway station? Can we use other expressions for that? And what about the preposition? Can we use 'in' instead of 'on' as 'on the train'?
4. You have to take the 9 a.m. train for Washington. ( Is this one right?)
5. How much is the bus fare?
How much is the subway fare?
How much is the taxi fare?
How much is the air fare?
How much is the train fare?
It is 20 dollars.
(Are the questions all correct?)
6. There are a vending machine and many slot machines in this building. You can enjoy gambling at a slot machine drinking coffee. First from the vending maching get a cup of coffee and sit in front of a slot machine. Just press the button on the slot machine. You can enjoy gambling.
(Is this sentence correct? Would you check wrong expressions?
7. How much is your school fee?
How much is the entrance fee?
How much is the membership fee of the helth center?
( Are the questions correct grammatically? Do we have to use 'fee' in this case? What other example sentences do you have?)
8. What is the price of the hat?
What is the price of the shirt?
(In this case, I have to use 'price', don't I?)
9. I am strong, ain't I?
I am strong, amn't I?
I am strong, aren't I?
(Which tag question is correct? Which one is frequently used?)
10. They can see subway signs everywhere in Seoul.
(Can we use 'everyplace' or 'anywhere' instead of'everywhere' in this sentence?)
11. I looked for my child.
11-1. I found my child.
(What is the difference between them?
Does #11 mean that I didn't found my child?)
11-2. I am finding my child.
(What about this one? Is this one the same as #11 in meaning?)
11-3. Look for my child.
11-4. Find my child.
(Are both the same?)
1. Both are OK.
2. All are OK, but I'd probably use the third one most of all.
3. The sentence is fine as it is -- no changes needed.
4. This sentence is fine. Some people use "A.M." instead of "a.m." for the abbreviation.
5. All are correct, yes.
6. There are many slot machines and a vending machine in this building. You can enjoy gambling at a slot machine while drinking coffee. First get a cup of coffee from the vending machine, and then sit in front of a slot machine. Just press the button on the slot machine. You can enjoy gambling.
I suggest putting "slot machines" before "vending machine" so that the plural form is closer to the plural verb "are." I also suggest putting "get a cup of coffee..." before "sit in front..." because that is the order in which those actions would be done.
7. All three questions are correct except for the spelling of "health." Yes, the word "fee" is needed. In using the word "fee," you could also ask questions like this: How much is the membership fee for this club?
8. Both questions are correct, and yes, you need to use "price of" -- or you could also say, "How much is the hat?" "How much is that shirt?"
9. Only the third one is correct. You might hear the first one, but it's slang and considered non-standard English!
10. The sentence is correct, and the substitutions you ask about can also be used. I think your sentence itself is the best one, though.
11. I looked for my child.
11-1. I found my child.
(What is the difference between them?
Does #11 mean that I didn't found my child?) Yes, that's right; #11 means I tried to find my child (but it's not clear whether I found him yet) and #11-1 means I found him.
11-2. I am finding my child.
(What about this one? Is this one the same as #11 in meaning?) It's very similar to #11; "am finding" is the present progressive tense, which means that when the sentence was spoken, the person was also in the process of finding the child.
11-3. Look for my child.
11-4. Find my child.
(Are both the same?) Yes