12/01/31 00:08:37.31
Each mattresses was originally 12cm thick,
but thickness is reduced by one third each time
an additional mattresses is piled on top.
のところ、英語間違ってるだろ。
but thickness is reduced by one third each timeのあとにカンマが必要で
そのあと、"and" an additional mattresses is piled on top.
とならないと文法的におかしい。