If 600 grams of 70% alcoholic solution is mixed with a gram of 40% final solution, the resulting alcoholic solution has a concentration of 62.5%, what is the value of a?
浓度为70%的酒精溶液600克与浓度为40%的究竟溶液a克混合后所得酒精溶液的浓度为62.5%，则a的值为多少．
<result>200</result>