作者nourri (nourri)
看板Statistics
标题[问题] 设random variable的问题
时间Thu Nov 4 01:26:35 2010
问题
The length of time before which a cell phone using the `Superdurable' battery
has to be recharged is normally distributed with a mean of 24 hours and a
standard deviation of 4 hours.
In order to avoid having his cell phone to run out of battery, a consumer
buys 4 `Superdurable' batteries. What is the probability that he does not need
to recharge his phone for 4 days?
我想问的是这题的四颗电池的variable要怎麽设
解答上是写 Y=X+X+X+X
但是为什麽不能设成Y=4X
谢谢
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1F：→ cisbpmtw:Y=X1+X2+X3+X4 X1...X4~N(24,4^2) 才对 11/04 13:11
2F：→ nourri:谢谢 11/04 13:17