Numbers are not only for numbers. In Chinese, the numbers appear in many set phrases to express various figurative meanings.
The vast majority of the set phrases with numbers are indicative of non-definite meanings, e.g. 五体投地 be awestruck with admiration. Only a small part of such set phrases express exact quantity.
Some of such set phrases express the meaning of “multi, plenty of, lots of, etc.”, for example, 千方百计 by all means; while others express “few, little”, e.g. 一毛不拔 unwilling to give up even a hair.
Some of them express the meaning of “complex, messy”, among which those with “七” and “八” are the most typical such as 横七竖八 in a mess.
Also, some of the set phrases with numbers have the function of highlighting and emphasizing, for example,一模一样 exactly the same.
More interestingly, some set phrases with numbers contain derogatory meanings, among which those with “三” and “四” are the most representative, for example, 低三下四 obsequious.