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A box contains 8 lightbulbs of which 3 are defective.A bulb

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A box contains 8 lightbulbs of which 3 are defective.A bulb is selected from the box
and tested.If it is defective,another bulb is selected and tested,until a nondefective
bulb is chosen.Find the expected number E of bulbs chosen.
同学,!难道你也在学AP统计?!
这是个典型的geometric distribution
一直重复实验直到第一次成功
E=1/p
p是成功概率,5/8
所以答案为8/5
如果要取整数的话是2