1. She has already bought the tickets.

2. She has bought the tickets already.
3. Already she has bought the tickets.
4. I am already ready to go out.
5. He already finished his homework.
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Which ones are correct?

2 and 5 are correct.

The others are not correct.

The correct sentences are:

1. She has already bought the tickets.
2. She has bought the tickets already.
4. I am already ready to go out.
5. He already finished his homework.

Sentences 1, 2, 4, and 5 are correct because the adverb "already" is correctly placed before the main verb in each sentence, indicating that the action or state occurred before the current moment. In sentences 1 and 2, "already" is placed after the auxiliary verb "has" and before the main verb "bought," which is the correct position in present perfect tense. In sentence 4, "already" is placed before the adjective "ready," emphasizing that the preparation has been completed before the current moment. In sentence 5, "already" is placed before the main verb "finished" in simple past tense, indicating that the homework was completed before the current moment.

Sentence 3, "Already she has bought the tickets," is not incorrect grammatically, but it is less common in English syntax. However, in cases where you want to emphasize "already," it can be used to place extra emphasis on the adverb.

Overall, the placement of "already" before the main verb generally fits best in English sentence structure.