I was watching a 西游记 adaptation from Little Fox Chinese and I've come across a sentence with numbers I can't quite understand. I read the translation but yet it doesn't make sense:
Guanyin looked at the messenger in surprise. "What is the problem?" she asked. "It's about the Tang Monk," said the messenger. "To become a buddha,he needs to face 81 challenges. I was just looking at the list of challenges he's faced."
This sentence 他得经历九九八十一难 doesn't make any sense to me, even worse when I look at the translation.
九九八十一 for me it looks like > 99811 How did it become "81" ??? (as seen in the translation)