If each shelf is to contain exactly 3 new CDs and there are only 5 shelves, only 15 can be placed in the rack. So, the answer to the second question is no. The same goes for the first question as placing 3 or fewer CDs to the shelves will make the rack insufficient for the CDs.
No, 2.3 is not bigger than 2.38.
In fact, 2.30 is less than 2.38.