Hi, thank you for your answer.
But the green and blue ball were not seprated from the other 8 balls.
And the propability of green ball is not 100% .
Would you explain it in detail ?作者: isenetlab12 时间: 2003-1-22 10:37
C8,2/c10,3=7/30
why C8,2? I see you mean the last two balls are chosen among the 8 other balls,but the first ball may be the blue one or one of the 8 balls since your formula did n't exclude these situations.
I think the answer should be 7/90.
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