三个数学题求解。 谢谢！

Q17: 这道题我死活看就是16% 答案说是25%

In Town X, 64 percent of the population are employed, and 48 percent of the population are employed males.  What percent of the employed people in Town X are females?

A.      16%

B.      25%

C.      32%

D.      40%

E.      52%

In Town X, 64 percent of the population are employed, and 48 percent of the population are employed males.  What percent of the employed people in Town X are females?

A.      16%

B.      25%

C.      32%

D.      40%

E.      52%

Q20:这个不太会做。可能是开放的公式忘记了。。。

If x > 0, then 1/[√(2x)+√x] =

A.      1/√(3x)

B.      1/[2√(2x)]

C.      1/(x√2)

D.      (√2-1)/√x

E.      (1+√2)/√x

In the xy-plane, point (r, s) lies on a circle with center at the origin.  What is the value of r² + s²?

(1)     The circle has radius 2.

(2)     The point (√2, -√2) lies on the circle.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

第一题分母是0.64

第二题选第四个，分母有理化，上下同时称以（2x）^1/2-x^1/2,化简

第三题也是第四个吧....说是这个点落在圆心在原点的圆上，根据圆的曲线方程直接就看出来了....(x-a)^2+(y-b)^2=r^2

(a,b)是圆心r是半径..

抱歉 我第一題還是有點不太懂ㄟ

如果分母是0.64那不就是0.64x0.52

請大大解答

percent of the population are employed femal =64 percent of the population (total employed)  -48 percent of the population (male employed)=16%

percent of the employed people in Town X are females=femal employed/total employed =16%/64%=25%