My textbooks says 八九不离十 means pretty close and that makes sense to me, but the way they use it makes me lose my head.
“汤姆说考试八九不离十就可以了。” I think they are trying to say " 80/90% is close enough", but the way they use it doesn't make sense to me at all. What is a better sentence that includes 八九不离十 in it? If it makes sense, could you explain why?
八九不離十 means almost there and I accept it or pretty close and I accept it, the most important thing is and I accept it. The ten may be perfect but if nine or eight are still fine.
“汤姆说考试八九不离十就可以了。” means Tom doesn't chasing for perfect in test.
First of all, “八九不离十” is very very informal. Even as a native speaker of Mandarin, I seldom use it. You should be careful when you want to use this phrase.
Secondly, Your example sentence “汤姆说考试八九不离十就可以了。” sounds very strange to me. I doubt a native speaker (at least in central mainland China) will use “八九不离十” in this way.
“八九不离十” means “相差无几” "差不多"，"very close to the fact but not exactly the fact"
你猜的八九不离十。 (Nǐ cāi de bā jiǔ bù lí shí.)
Your guess is pretty close.
Update: An analysis of “八九不离十”
“八” = number 8 “九” = number 9 “不” = not “离” = "far away from" “十” = number 10
Literally, “八九不离十” means "number 8 and 9 are not far from number 10", "number 8 and 9 are pretty close to number 10", so it is used to mean "very close to the fact but not exactly the fact".
I’m not sure that the term is used correctly in “汤姆说考试八九不离十就可以了”. According to the dictionary, “八九不离十” means “nearly approaching the fact”, and using “fact” to describe exam results is not appropriate, so the sentence makes sense but isn’t grammatically right.
Here’s an example that the term is correctly used:
他猜得不对，但是八九不离十了。
He guessed wrong, but is almost there.
For simple, replace it with 差不多. But the point is:
To understand what object/target is close to, or what 十 (the object) represents in the sentence.
这电影不好看，跟我之前想的八九不离十（差不多）
十 represents 不好看(boring)
The movie is boring anyway.
这次考试结果，她能猜个八九不离十（差不多）
十 represents 考试结果(score)
She guessed a close number.
汤姆说考试八九不离十（差不多）就可以了
Tom can accept an average score.
So the trick is, 十 represents 通过(passed) in the sentence, NOT Excellent(A+)
Remember 十 is just an object, NOT a number, NOT ten out of ten, and Tom just wanna pass the exam.
