单选题 How many gallons of water must be mixed with 1 gallon of a 15-percent salt solution to obtain a 10-percent salt solution?
(A) 0.50 (B) 0.67 (C)1.00
(D) 1.50 (E) 2.00

【正确答案】 A
【答案解析】[解析] 设必须加入x加仑的水，根据题意可得：
(1+x)×10%=1×15%→x=0.5