GWD 11

Q36: （求解思路。。。）

If x, y, and k are positive numbers such that (x/（x+Y )}(10) +（Y/（x+Y））（20) = k and if x < y, which of the following could be the value of k?

A.      10

B.      12

C.      15

D.     18

E.      30

Answer: D

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k=10+10y/(x+y)

令y/(x+y)=a, 则a<1, 且x<y, x+y<2y => 10a>5

so  15<k<20