Question:

How can we calculate the actual number of plates which Joseph Smith received from Moroni? 

Answer:

The secret to this may also be in the number 24. There is some evidence that Mormon's abridgment took 24 plates. That being so, the sealed portion, etc, must have taken around 48 plates. This totals 72 plates, which also is a unique number in the Book of Mormon. (See 3 Nephi 28:3)