两道GWD的吐血题

Q36

If x, y, and k are positive numbers such that ( x)(10)/(x + y) + ( y)(20)/(x + y) = 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

Ans: D

请问这题怎么解勒?? 我找到两种方法
                其中一种方法
                我怎么看都无法把式子化解
                另一种方法我绝得是不可行的
                

请大家帮我解一下
                若是用化简的
                麻烦请帮我写一下详细的式子
                我很逊拉!!

Q10

     The sides of a square region, measured to the

         nearest centimeter, are 6 centimeters long. The

         least possible value of the actual area of the

         square region is

A.36.00 sq cm

B.35.00 sq cm

C.33.75 sq cm

D.30.25 sq cm

E.25.00 sq cm

Ans: C

不知这题如何解??

36.上面式子化简成 10+(10Y)/(X+Y)=K

0<x<y  又有10Y/(Y+Y)<10Y/(X+Y)<110Y/Y

即 5<10Y/(X+Y)<10

所以 15<Y<20

10. 题意是正方形的边长精确到个位数是６ＣＭ，问实际面积最小是多少

四舍五入能到６的最小数是５．５，５．５的平方

是我傻拉!! 怎么样化简成上面绿色的式子啊!! 我怎么化都化不出来
                为什么大家一开始就可以跳到那一步骤呢
                ?? 怎么办到的??
                

所以第二题
                是答案给错啰!! ??

yes, the second quesiton is D, have discussion before.

sorry i don't remember which GWD...