Two hundred milliliters of pure water is added to 300 milliliters of a solution which is 12% salt. What is the percentage of salt in the resulting solution?
6.0%
6.5%
6.9%
7.2%
7.5%
根据浓度公式可知，现在的浓度=(12%×300)/(200+300)=7.2%，故本题选D项。