How old was Shem when he begat Arphaxad?

"I have a question and don't know shall I stick to scuh details or not, or it might be a translation question: How old was Shem when he begat Arphaxad? in Gen 5:32, And Noah was five hundred years old: and Noah begat Shem, Ham, and Japheth. And in Gen 7:11 when flood came Noah was 600 year old. But in Gen 11:10, Shem [was] an hundred years old, and begat Arphaxad two years after the flood: Does this mean Shem only was 98 years old when flood came? But according to Gen 5:32 and 7:11, Shem should be 100 years old already. thank you."

Dear Sister:

Praise the Lord that you pay attention to details. You are right that most of translations including Chinese Union Version (和合本) and King James Version did not accurately translate Gen 11:10. So that’s why we need Faith Version (信實本):

(Faith Version) Gen 11:10 These [are] the generations of Shem: Shem begat a son at one hundred years old, and begat Arphaxad two years after the flood:

In Gen 11:10: Shem begat a son at one hundred years old: the son was Elam (Gen 10:22). Arphaxad is the 3rd son of Shem. So when Arphaxad was born, Shem was 102 years old.

Make sense now? Praise the Lord that he is faithful and makes no mistake! Amen.