GWD 11 MATH Q23 HELP!

dreamlollipop

Q23:
One kilogram of a certain coffee blendconsists of x kilogram of type I coffee and y kilogram of type II coffee.  The cost of the blend is C dollars perkilogram, where C = 6.5x + 8.5y.  Is x< 0.8?
(1)       y > 0.15
(2)       C ≥ 7.30
                 
A. Statement (1) ALONE issufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient,but statement (1) alone is not sufficient.
C. BOTH statements TOGETHERare sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE issufficient.
E. Statements (1) and (2) TOGETHERare NOT sufficient.

jingyunhua

选e 1＋2能求出 x小于0。927，但不能保证小于0。8

terryhan

x=(C-8.5y)/6.5，因为y只有下限，C也是只有下限，两个变数可以同时增大，所以不能确定x的极值。

zyzfrank

是选B吧？
第一句话隐含的条件是x+y=1

matthewliu1981

B.   X+Y=1

yfan2

选e。 x+y=1， c=6.5（1-y）+8.5y  goes to c=6.5+2y, if y>0.15 , x<0.85; if c>7.3, y>0.4, so x<0.96. no evidenc can support x<0.8. E is correct.

zyzfrank

选e。 x+y=1， c=6.5（1-y）+8.5y  goes to c=6.5+2y, if y>0.15 , x<0.85; if c>7.3, y>0.4, so x<0.96. no evidenc can support x<0.8. E is correct.

-- by 会员 yfan2 (2010/11/21 1:29:17)

C = 6.5x + 8.5y  x+y=1  goes to C=6.5x+8.5(1-x)=8.5-2x;  if c>7.3 ,so 8.5-2x>7.3 ,x<0.6.So the answer is B.

sdluolei

B，X取值0到1，Y是1到0. C的range 是6.5到8.5. 当X=0.8的时候，C取值6.9.所以，当C》6.9时，X必定小于0.8