甲口袋中有大小质地都相同的白球3个,红球5个；乙口袋中有大小质地都相同的白球4个,黑球8个.从两个口...甲口袋中有大小质地都相同的白球3个,红球5个；乙口袋中有大小质地都相同的白球4个,黑球8个.从两个口袋各摸出2个球,求：两个口袋中摸出4个球里恰好有2个白球的概率?

可分以下几种情况：1.白球全部来自甲 2.其中一个来自甲，另一个来自乙。3.两个全来自乙= (C(5,2) * C(4,2) + C(3,1) * C(5,1) * C(4,1) * C(8,1) + C(3,2) * C(8,2))/(C(8,2) * C(12,2))
=154分之52

(Reporter intern at Tian Chi Xin Xin) 2010, Tianjin, China Baseball League game last night at Dodger stadium baseball games continue, Tianjin Lions lost the first day swept away the haze, to 18 to 3 victory over the dragon Sichuan team, usher in a new first victory of the season. The campaign team of young free hand in Tianjin, a start will set off a wave of attack, the opponent hit a three bureau 12 to 0. Surprise team in Sichuan began to catch up in the fourth inning, the fourth Jushang Ban Bureau Lianban 2, Tianjin team returned from the Bureau of Yao Junlei half in the fourth scored 1 point. Team of Sichuan Bureau of the fifth Jushang Ban then 1 minute, but then did not give the other team in Tianjin any chance, and half in the fifth Bureau won 5 consecutive homerun, they will have only 18 minutes of five, ahead by 15 points early end to the fighting. This hearty victory for the boys team in Tianjin to restore self-confidence, coach Takagis face also revealed long-lost smile. He said that both the overall individual play or team tactics, Tianjin team are to overwhelm the opponent, attack and defense is very good. Takagi said excitedly: "I am confident that with a team back to the top level of our main goals is the National Games 2013, a year or two back to previous levels though a bit difficult, but certainly three or four years to build a king of the division. "(Editor: zhaolangxing)
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48_566

48_510

48_661

= (C(5,2) * C(4,2) + C(3,1) * C(5,1) * C(4,1) * C(8,1) + C(3,2) * C(8,2))/(C(8,2) * C(12,2))
= 0.337662337

10分之3