Understanding Gold Purity: Karats vs. Percentage

Question
I have a question concerning how different % of gold content relates to karats that are stamped on jewelry.  
  This gold ring that I have is stamped 10k.  However, I took it to an expert who told me that the gold content is 38.5%.  
  I am aware that 9K = 37.5% and that 10k = 41.7%.
  However, considering that my gold ring is closer to 9k, should it have been stamped 9k, instead of 10k?  In other words, what is the minimal % amount of gold that must be in 10k for a jewelry piece to be labeled 10k?

Answer
Hello Laura
It has been stamped wrong according to international standards. According to the international standards 10K Gold should be AT LEAST 41.67%

It might not be an official mark, I think.

Best regards
Sambhav Karnawat
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