CLAIM: Different translations render this number differently: The NKJV and AV say it is “one year.” The NASB and ASV say Saul was “forty” when he began to reign. The RSV simply leaves this section blank. Which is correct?
SOLUTION: This number is missing in the original Hebrew text. The text literally states, “Saul was a son of… years when he became king, and he ruled for two years in Israel.” This is why various translations render this differently. They are trying to infer what the original text stated. The number must be over twenty, because a number of nineteen or below would have grammatically required the plural (sanim). Archer writes, “Because the singular sanah is used here, we can tell that a numeral of twenty or more must have preceded it.”
 Archer, Gleason L., and Kenneth S. Kantzer. Encyclopedia of Bible Difficulties. Grand Rapids, MI: Zondervan, 1982. 170.