3題probability

2008-05-18 10:36 pm

1.There are three pairs of red socks, two pairs of white socks and two pairs of blue socks in a dawer. Two socks are draw at random without replacement. Fnd the probability that the socks draw are
(a)one red and one blue,
(b)of differen colours,
(c)of the same colour.

2.Six balls numbered -6,-4,-2,2,4 and 6 are put in a bbag. If two balls are drawn randomly without replacement, find the probability that the sum obtained is 0.

3.Two dice are thrown. Find the probability that the sum of the numbers is greater than 8 given that one of them is a '5'.

要步驟THX

回答 (1)

Rainbo

2008-05-18 11:14 pm

✔ 最佳答案

1.
a. P(1R1B) = 6/14 x 4/13 + 4/14 x 6/13 = 24/91
b.
P(diff colours)
= 1 - P(same colours)
= 1- ( 6/14 x 5/13 + 4/14 x 3/13 + 4/14 x 3/13 )
= 64/91

c. P(same colours) = 6/14 x 5/13 + 4/14 x 3/13 + 4/14 x 3/13 = 27/91

2.
P(sum is 0) = 6/30 = 1/5

3.
P(sum is greater than 8 with one '5') = 5/11

I got the ans2 and ans3 by graphing. Sorry that I still dont know how to provide u the written steps. >

參考: 自己計算

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