求问2题数学

xyzxf

Store S sold a total of 90 copies of a certain book during the seven days of last week, and it sold different numbers of copies on any two of the days. If for the seven days Store S sold the greatest number of copies on Saturday and the second greatest number of copies on Friday, did Store S sell more than 11 copies on Friday? (1) Last week Store S sold 8 copies of the book on Thursday. (2) Last week Store S sold 38 copies of the book on Saturday.

One kilogram of a certain coffee blend consists of x kilogram of type I coffee and y kilogram of type II coffee. The cost of the blend is C dollars per kilogram, where C = 6.5x + 8.5y. Is x < 0.8 ? (1) y > 0.15 (2) C 〉=7.30

lunasea

第一道题目 因为sold different numbers of copies on any two of the days.
我的理解是 任意抽2天销量都不一样=每天销量不一样
我觉得主要的问题是C是否可能存在（2条件合并是能求的周五>11 ）

假设周五销量等于11  周四的销量等于8  周六等于38  
由于周六 周五排在销量前2位
也就是说 周1~3  以及周日的每日销量都要<11 并且排除8
TOTAL-FRIDAY-SATURDAY-THURSDAY=33
也就是说 周1~3 以及周日 可以去1~7，9~10 中任意整数 并且不能重复
取出其中最大的四个数字 10 ，9 ，7， 6  求和  SUM=32
达不到33 也就说 在2个条件连立的情况下 周五销量一定要超过11
才能满足TOTAL=90

lunasea

第二题
因为1KG混合=X+Y   所以 X=1-Y
C=6.5(1-Y)+8.5Y
先做条件2哈
设C=7.3    
7.3=6.5(1-Y)+8.5Y    Y=0.4   X=0.6 <0.8
条件1 Y>0.15
由于原式=6.5（1-Y)+8.5Y  =6.5+2Y  
个人认为 Y 的取值 无法影响到X <0.8  
我计算过当Y=0.15 X =0.85 时   C=6.8