请教~非常感谢你的concern

sasha1124

Q9:

A gardener is going to plant 2 red rosebushes and 2 white rosebushes.  If the gardener is to select each of the bushes at random, one at a time, and plant them in a row, what is the probability that the 2 rosebushes in the middle of the row will be the red rosebushes?

 

A.     1/12

B.      1/6

C.      1/5

D.     1/3

E.      1/2

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

Each signal that a certain ship can make is comprised of 3 different flags hanging vertically in a particular order.  How many unique signals can be made by using 4 different flags?

 

A.     10

B.      12

C.      20

D.     24

E.      36

geminisky

第一题：种第一个是白色概率：1/2，第二个是红色：2/3，第二个是红色：1/2，

答案：1/2×2/3×1/2＝1/6

第二题：1/[√(2x)+√x] ＝[√(2x) - √x]/ (2x-x) =
                                (√2-1)/√x

第三题：P(4,3)=24