Donald W. Parry explains a Hebraism in the Book of Mormon:
Often in biblical Hebrew, an expected noun does not follow a number. For instance, Genesis 45:22 states that Joseph “gave three hundred of silver” to Benjamin, without stating that the three hundred probably refers to pieces of silver. In order to fix what would have been an awkward omission in English, the King James translators supplied the word pieces but italicized it to show that it is not part of the original text. Other biblical examples of the number without the noun include “ten weight of gold” (Genesis 24:22; the KJV adds shekels to its translation: “ten shekels weight of gold”), “he measured six of barley” (Ruth 3:15; the KJV adds measures: “he measured six measures of barley”), and “a captain of fifty with his fifty” (2 Kings 1:9).
In the Book of Mormon, Laman and Lemuel ask, “How is it possible that the Lord will deliver Laban into our hands? Behold, he is a mighty man, and he can command fifty, yea, even he can slay fifty; then why not us?” (1 Nephi 3:31). The number fifty, used twice in this passage, is not followed by a noun. Does fifty refer to men, warriors, princes, commanders of armies? The context does not make this certain. Other Book of Mormon examples include “my little band of two thousand and sixty fought most desperately” (Alma 57:19); “Wherefore, by the words of three, God hath said, I will establish my word” (2 Nephi 11:3); “And it came to pass that there were two hundred, out of my two thousand and sixty” (Alma 57:25).– Donald W. Parry, “Hebraisms and Other Ancient Peculiarities in the Book of Mormon,” in Echoes and Evidences of the Book of Mormon, edited by Donald W. Parry, Daniel C. Peterson, and John W. Welch (Provo, Utah: FARMS, 2002), Chapter 7
Wouldn’t we expect Joseph Smith to add in the noun whenever he mentioned a number?