1. I often go skiing with my friends on weekends.

2. I often go skiing with my friends weekends.

3. I often go skiing with my friends on the weekends.

4. I often go skiing with my friends on the weekend.

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Are they all grammatical? Would you let me know incorrect expressions?

2 answers

You don't need to answer it?.There was a problem. I posted the qeustion, but I could not find the quetion after I clicked Current Questions. So I posted this question again. ..Later I pressed the refresh butten. Then I could see the posted questions.
SraJMcGin is right. All the sentences are good except for #2. It isn't incorrect; it just isn't used very often.