How to use "one(s)"?

[Nhung]

Can you tell me how to use "one(s)"?I have known that it is used to replace for the precedent nouns .But in some cases ,it is impossible to do like that.
Ex:On one channel was a war film and on the other was a horror film,so I turned the TV off .
So I want to know more about the usage of "one(s)".Can you?

[Mister Micawber]

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The best place to start, nhung, is a dictionary, which often includes examples:

One (pronoun)

16. a person or thing of a number or kind indicated or understood: one of the Elizabethan poets.
17. (in certain pronominal combinations) a person unless definitely specified otherwise: every one.
18. (with a defining clause or other qualifying words) a person or a personified being or agency: the evil one; the one I love.
19. any person indefinitely; anyone: as good as one would desire.
20. Chiefly British. (used as a substitute for the pronoun I): Mother had been ailing for many months, and one should have realized it.
21. a person of the speaker's kind; such as the speaker himself or herself: to press one's own claims.
22. something or someone of the kind just mentioned: The portraits are fine ones. Your teachers this semester seem to be good ones.
23. something available or referred to, esp. in the immediate area: Here, take one—they're delicious. The bar is open, so have one on me!
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Native English teacher at Mister Micawber's

[Nhung]

Oh,I think I didn't make you understand what I wanted to ask
Today,I am giving my exercises to you .
**If appropriate ,replace the underlined words or phrases with one or ones .If it's not possible or unlikely ,write No after the sentence.
1)If you 're buying a newspaper from the shop ,could you get a newspaper for me ?----one
2)He used to work for a finance company ,but he moved to an insurance company----NO
3)Many people are happy about the new road being built ,but there are some angry people ,too----NO
As you see, each above sentence has an enclosed answer.But I don't understand why they do like that.So I wanna to ask you to give me the rule of replacing "one(s)" because in my dictionary and even grammar book ,they don't mention how to replace
*I hope you can understand what I want to ask.
Thank you for your fast reply.

[Mister Micawber]

1) If you're buying a newspaper from the shop, could you get one for me?-- OK
2) (X) He used to work for a finance company ,but he moved to an insurance one----No, we do not usually use 'one' after a modifier.

3) (?) Many people are happy about the new road being built, but there are some angry ones, too-- I think this is possible, even though it follows a modifier.

Please remember that commas and other similar punctuation marks are followed by a blank space, but there is no blank space before them.
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Native English teacher at Mister Micawber's

[Duc]

Now I give you some useful usage of ONE/ONES:
We don't use one/ones:
• after a - instead we leave out a:
• Have we got any lemons? I need one for a meal I'm cooking, (not ...need a one...)
• after nouns used as adjectives:
• I thought I'd put the keys in my trouser pocket, but in fact they were in my jacket pocket.
(not ...my jacket one.)
Instead of using one/ones after personal pronouns (my, your, her, etc.) we prefer mine, yours,
hers, etc. However, a personal pronoun + one/ones is often heard in informal speech:
• I'd really like a watch like yours, (or '...like your one.' in informal speech)
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Don't see your shade think you are great

[Nhung]

• after nouns used as adjectives:
• I thought I'd put the keys in my trouser pocket, but in fact they were in my jacket pocket.
(not ...my jacket one.)-------Can you check them more carefully in this case? Because I can see this case in some following sentences:
1. Would you make a copy for everyone in the office and a few extra ones for the visit.
2.I answer most of the question, but had to miss out some very difficult ones
Thank Mister Micawber for the useful advice!

[Duc]

ha,you need to read carefully.''Nouns used as adjectives'' but not adjectives and ''extra'',''difficult'' are adjectives.
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Don't see your shade think you are great

[Nhung]

uh-huh,thank you for your reply very much^^.