（4分）某同学想用天平、量筒尽量准确地测量出桌上一烧杯内的盐水的密度，请你帮他设计这个实验，并写出实验步骤和盐水密度的表达式。
实验步骤：
盐水密度表达式：
.实验步骤：
①在烧杯杯中盛适量盐水，用天平称出它们的质量m1，并记录在表格内；
②把烧杯中的盐水倒入量筒中一部分，用量筒测出盐水的体积V，并记录在表格内；
③再用天平称出烧杯和剩余盐水的质量m2，并记录在表格里。
盐水密度表达式：
分析：用天平和量筒测量液体的密度，其依据的原理就是密度的公式ρ=
，因此，在实验设计时应围绕这一原理展开．为了减小误差，在步骤安排时，应重点考虑避免因液体的倾倒而产生的对测量结果的影响．
解答：解：实验步骤：
①在烧杯杯中盛适量盐水，用天平称出它们的质量m1，并记录在表格内；
②把烧杯中的盐水倒入量筒中一部分，用量筒测出盐水的体积V，并记录在表格内；
③再用天平称出烧杯和剩余盐水的质量m2，并记录在表格里．
盐水密度表达式：ρ盐水=
故答案为：（1）实验步骤同上；
（2）盐水密度的表达式：ρ盐水=．
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| When you read this sentence, the population of the earth has grown by 10 people. 1.________ Most of these new people are born in developing countries. 2.________ In the developed countries of Europe and North America, the population is growing very slowly. This is because women in these countries have, on average (平均), only one or two children. 3.________ In the developing countries, more than one billion people already live below the poverty line (贫困线). 4.________ Children get little or no time at school and suffer from many kinds of diseases. The UN has said that the world's population will reach 12.5 billion people by the year 2100. If the number makes your head spinning (眩晕), you're not alone. Many experts are worrying that so fast population growth could have very bad results. 5.________
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