小丁每天从某报社以每份0.5元买进报纸200份，然后以每份1元卖给读者，报纸卖不完，当天可退回报社，但报社只按每份0.2元退给小丁，如果小丁平均每天卖出报纸x份，纯收入为y元．
（1）求y与x之间的函数关系式（要求写出自变量x的取值范围）；
（2）如果每月以30天计算，小丁每天至少要卖多少份报纸才能保证每月收入不低于2000元？
（1）y=（1-0.5）x-（0.5-0.2）（200-x）
=0.8x-60（0≤x≤200）；
（2）根据题意得：
30（0.8x-60）≥2000，
解得x≥158
．1 3
故小丁每天至少要卖159份报纸才能保证每月收入不低于2000元．
从下边的方框中选择最佳选项填入空白处，完成对话。（共5小题，每小题1分）
B: 小题1: I can't do any work, doctor. A: Do you have a cold? B: No, I don't have a cold. A: 小题2: B: Yes, I always sleep very well. A: Do you have breakfast every morning? B: No, I don't have breakfast. And I have only a little food for lunch and supper because I want to keep thin. A: Oh, I see. 小题3: You need to eat more food and have three meals a day. 小题4: B: Ok. I will do like that. A: 小题5: B: Thank you very much. |