临江仙 · 2020年08月16日
问题如下：
600 table tennis balls are placed in a black box, three of which are written with different words. On a random draw, what is the probability that one of these 3 balls will be drawn?
选项：
A.0.004.
B.0.005.
C.0.010.
D.0.008.
解释：
B is correct.
考点：Basic probability calculation
解析：P(ball1 or ball 2 or ball 3) = 1/600 + 1/600 + 1/600 = 3/600 = 0.005
我的思路有问题吗：
600个球分为597个正常和3个特别
然后从600个抽取3个球，可以分为597个球里抽取2个，3个球里抽取1个。
那么P应该是 C597-2*C3-1/C600-3
NO.PZ2019040801000007 问题如下 600 table tennis balls are placein a blabox, three of whiare written with fferent wor. On a ranm aw, whis the probability thone of these 3 balls will awn? A.0.004. B.0.005. C.0.010. 0.008. B is correct.考点Basic probability calculation解析P(ball1 or ball 2 or ball 3) = 1/600 + 1/600 + 1/600 = 3/600 = 0.005 根据加法法则，P(A or B or C)=P(A or B)+P(C)-P(A or B * C)=P(A)+P(B)-P(AB)+P(C)-P(A or B * 对吗？P(A or B or C)为什么等于1/600+1/600+1/600
为什么不是3C1*(1/200)*(199/200)*2？
