试题与答案

已知盐水若干千克,第一次加入一定量的水后,盐水浓度变为6%,第二次加入同样多的水后,

题型:单项选择题

题目:

已知盐水若干千克,第一次加入一定量的水后,盐水浓度变为6%,第二次加入同样多的水后,盐,水浓度变为4%,第三次再加入同样多的水后盐水浓度是( )。

A.3%

B.2.5%

C.2%

D.1.8%

答案:

参考答案:A

解析: 开始给出的盐水既没有重量,也没有浓度,可以不予考虑。从第一次加水后算起,用特殊数值法。设第一次加完水后有盐水100克,其中含盐6克,第二次加人同样多的水后,盐水浓度变为4%,可得盐水质量为=150克,所以加水为150-100=50克;冉加入50克水,盐水总重量为150+50克,盐水浓度为。故选A。

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