1. I read comic books, eating some snacks.
2. I read comic books while /as I ate some snacks.
3. I read comic books and ate some snacks.
4. I read comic books and ate some snacks at the same time.
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Are they all the same and grammatical?
Does #3 mean #1 without adding 'at the same time' at the end?
Is "read" in these sentences intended to be the past tense? (pronounced "red")
Yes. It's the past tense.
All the sentences are fine. They'd be better if you added "Last night" or some other phrase that indicates past tense.
All four sentences you provided are grammatically correct, but they convey slightly different meanings:
1. "I read comic books, eating some snacks."
This sentence suggests that you read comic books while intermittently eating snacks, but it does not necessarily imply that you are doing both activities simultaneously.
2. "I read comic books while/as I ate some snacks."
This sentence indicates that you are engaged in the act of reading comic books while simultaneously eating some snacks. It conveys the idea of performing both activities at the same time.
3. "I read comic books and ate some snacks."
This sentence means that you engaged in the activities of reading comic books and eating snacks, but it does not explicitly denote that you did both activities simultaneously. This sentence can be understood as doing one activity and then doing the other separately.
4. "I read comic books and ate some snacks at the same time."
This sentence emphasizes that you performed both activities simultaneously. It suggests that you were reading comic books and eating snacks concurrently.
So, to summarize, sentence #3 can be seen as similar to #1 but without explicitly mentioning doing the activities at the same time. Sentence #4 makes it explicitly clear that both activities were happening simultaneously.