Foreigners often make some strange mistakes in Chinese when they study the most difficult language--- ---Chinese. We try to analyze typical sentences to correct these errors.

          Tā yǐjīnɡ zhùyuàn shí sì jǐ tiān le.
False: 他已经住院十四几天了。
          Tā yǐjīnɡ zhùyuàn shí sì wǔ tiān le.
True: 他已经住院十四五天了。

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.