求助一道DS题~~~~~~~~~~

oliviading

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 ≥ 7.3

Answer: E-->B

可是,B根本就算不出x < 0.8是否满足的条件呀~~因为C可取无限大了,那么x既可以>0.8也可以<0.8都没有问题呀,,,不是么???

求助各位指点迷津~~

oliviading

Oh~~~Yup...Thank you very much!!!

littlestoner

x+y=1,so c=6.5x+8.5y=6.5x+8.5(1-x)=8.5-2x>=7.3

so x<=0.6

right?

susanyakis

One kilogram of a certain coffee blend consists of x kilogram of type I coffee and y kilogram of type II coffee

《=》x+y=1