Do those sentences have the same meaning?

[shuei]

I am a junior high school student in Osaka, Japan.

I have learned these sentences:
1. A year has twelve months.
2. There are twelve months in a year.
3. We have twelve months in a year.

What is the difference between them?
Do they have the same meaning?

Please help me.

[Alamshar]

They all have the same meaning. I wouldn't use no.3 though as it doesn't sound natural

[5jj]

1. A year has twelve months.
2. There are twelve months in a year.
3. We have twelve months in a year.

They all have the same meaning, and they are all grammatically acceptable. #2 is the most natural, #1 is possible, and #3 is unlikely to be said, in my opinion.

[acomber]

2. should be preferred - it is more formal than 1. You might use 1. more in speech.

3. We have twelve months in a year. Doesn't sound right to me. It is not them that has 12 months! It is the year that is made up of 12 months.

[shuei]

Thank you very much for your lessons, teachers!

I have been feeling that # 3 doesn't sound natural.
I thought that # 3 could be heard during a conversation with aliens from outer space...

[5jj]

I thought that # 3 could be heard during a conversation with aliens from outer space...

Absolutely. So could, "*^#@..><#"