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.

          Nàshì èrshí sān fēn liù.
False: 那是二十三分六。
          Nàshì èrshí sān fēnzhī liù.
True: 那是二十三分之六。

汉语用“……分之……”表示分数，应当在分后补上不可少的之。
“分之” is the formula to indicate fractions in Chinese. 之 is obligatory after 分.