| 答案 |
| 送交者: 车五进二 2019月12月19日19:53:50 于 [灵机一动] 发送悄悄话 |
| 回 答: 趣味的数学-201 由 gugeren 于 2019-12-13 00:36:12 |
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There are 19 positions that B/G combination may accur, for each position, the probability of BG or GB is (7*13*2)/(20*19)=91/190, therefore the expect number of B/G combination in a lineup is 19 * (91/190) = 9.1, closest to 9. |
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