三十

guò qù sān shí nián lái shè huì xí sú yǒu le hěn dà de biàn huà

过去三十年来，社会习俗有了很大的变化。

The last thirty years have seen great changes in social mores.

tā zǒu dào sān shí gōng chǐ wài yòu huí tóu kàn

他走到三十公尺外又回头看。

He looked back when he had gone thirty metres.