Jim's and Mary's room

[sitifan]

According to English Grammar Code by Wang Shengliang, page 11, the expression "Jim's and Mary's room" refers to two rooms -- one is Jim's, the other is Mary's.
Do native speakers agree with what he says?

 

[5jj]

No.

Jim and Mary's room - one room.
Jim and Mary's rooms - two (or more) rooms shared by two people.
Jim's and Mary's rooms - two (or more) rooms not shared.

 

[slevlife]

To be more explicit about the case that 5jj left out ("Jim's and Mary's room"), native speakers would not say this. But if they did, it would be understood the same as "Jim and Mary's room" — it's one room that they share.

 

[Phaedrus]

According to English Grammar Code by Wang Shengliang, page 11, the expression "Jim's and Mary's room" refers to two rooms -- one is Jim's, the other is Mary's.
Do native speakers agree with what he says?

For that interpretation, which is conceivable and grammatical, assuming ellipsis is intended, I would need to hear extra stress on "and Mary's":

Jim's AND MARY'S room are both on the same floor.
= Jim's [room] and Mary's room are both on the same floor.

Compare:

Jim's room and Mary's are both on the same floor.
= Jim's room and Mary's [room] are both on the same floor.

 

[emsr2d2]

And bear in mind that most native speakers would say "Jim's room is on the same floor as Mary's".