有这样一道竞赛题: 已知由CuO与Cu_2S组成的混合物中,当硫元素的质量分数为10％时,氧元素的质量分数也为10％;当硫元素的质量分数为15％时,氧元素的质量分数为______. 很多考生不经思维就填写出“15％”(占73％),还有部分考生答案为“25％”(占10％)和“5％”(占17％)。收集考试用草稿纸,归纳有下列五种解法。 There is such a contest title: It is known that the mixture composed of CuO and Cu 2 S, when the mass fraction of sulfur is 10%, the mass fraction of oxygen is also 10%; when the mass fraction of sulfur is 15%, oxygen The mass fraction of the elements is _______. Many candidates fill out “15%” (73%) without thinking, and some candidates answer “25%” (10%) and “5%” (17%) ). Collect draft papers for examinations and summarize the following five solutions.