Tom and John's rooms are different的错

Tom's and John's rooms are different

原句意为二人共有的房间,应改为Tom's

tom and john's表示他们共有的,所以不能不同

原句意为二人共有的房间
更加合理的表达是：
The rooms of Tom and John are different.

这就意思是说tom 和 john共同的房子。可以换个说法，tom's room is different from john's (room).

Tom's and John's rooms are different