When communicating in Chinese you may often make mistakes using Chinese grammar like:

False:

    他已经住院十四几天了。

    Tā yǐjīnɡ zhùyuàn shí sì jǐ tiān le

True:

    他已经住院十四五天了。

    Tā yǐjīnɡ zhùyuàn shí sì wǔ tiān le

 

汉语表示概数的方式之一是相邻的两个数目连用，表示大概的数量，可以说十三四，四五十。几本身是个概数，不能与定数四连用，根据两个相邻数目表示概数的要求，应当删去几，改成十四五。

One way to express approximate numbers in Chinese is to use two adjaccent digits together. We can say 十三四，四五十.几 itself represent an approximate number and never occurs next to a definite number such as 四. According to this rule, we change 几 into 五, i.e. 十四五.