问题
单项选择题
How many liters of pure alcohol must be added to a 100-liter solution that is 20 percent alcohol in order to produce a solution that is 25 percent alcohol ？（）
A.A
B.B
C.C
D.D
E.E
答案
参考答案：C
解析：
设需加入x升的纯酒精，根据题意可得
升。