幫指點個機率問題

h5641 · 发表于 2009-4-21 14:34:00

Q37:

A jar contains 16 marbles, of which 4 are
red, 3 are blue, and the rest are yellow.
If 2 marbles are to be selected at random from the jar, one at a time
without being replaced, what is the probability that the first marble selected
will be red and the second marble selected will be blue?

A.
3/64

B.
1/20

C.
1/16

D.
1/12

E.
1/8

Answer:

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哪位好心大俠幫指點一下想不出來阿~　　傷心阿～

h5641 · 发表于 2009-4-21 14:49:00

想到了

4/16 * 3/ 15 = 1/20

原來是這樣... 原方向都錯了...　>__<

h5641 · 发表于 2009-4-21 15:22:00

另外一題　一樣的觀念　　如果有跟我一樣笨的人（希望沒有）可以一起分享：

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

Answer:

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從一方向

1/4 (第一次拿白）

2/3 (第二次拿紅）

1/2 (第３次拿紅）

1/4 * 2/3 * 1/2 = 1/12

從另一方向亦同　所以　1/12 * 2 = 1/6

幫指點個機率問題

幫指點個機率問題

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