workhard77

设水x, 则dry part=(volume of tatle liquid)-x,
20%=x/[(volume of tatle liquid)-x]

workhard77

求湿度的百分比，等于ratio of water and dry part of a liquid，然后告诉你液体的总量，问你水是多少时，那个比率是20％

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仅仅是我的理解：
湿度=（volume of water in the liquid)/(volume of dry part in the liquid)
不是很确定，还是请版主看看吧。