cjrylant wrote:

gamjatang wrote:

Total flowers : AA, BBB, PPPP

Probability that two same flowers are picked:

AA = 2/9 * 1/8 = 1/36

BB = 3/9 * 2/8 = 1/12

PP = 4/9 * 3/8 = 1/6

--------------------------

1/36 + 1/12 + 1/6 = 5/18

1 - 5/18 = 13/18

Thus, 13/18

Thanks for the help. 13/18 is the answer in the book but I cant see how to get to it.

Where do you get the "*1/8" "*2/8" "*3/8"

// cjrylant

There are 9 flowers now.

After you pick one, then there are 8 flowers left.

Likewise, there are 4 PPPP now.

After you pick one P, then there are three PPP left.

That's where "1/8", "2/8", and "3/8" came from.

// duttsit

If you pick two flowers at one time, the result will be the same.

The formula will be like following (and is much more time-consuming);

1) Total number of possible picks

= 9C2 = 9*8/2=36

2) Possible number of cases in which two A's are picked

= 2C2 = 1

2) Possible number of cases in which two B's are picked

= 3C2 = 3

3) Possible number of cases in which two P's are picked

= 4C2 = 6

-----------------------------------------------------------------

From 1), 2), 3), and 4), we can see that the possibility of picking two same flowers is (1+3+6)/36 = 10/36 = 5/18

Thus, the possibility of picking two different flowers is 1 - 5/18 = 13/18.

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Auge um Auge, Zahn um Zahn !