12. In a certain animal population, for each of the first 3 months of life, the probability that an animal will die during that month is 1/10 . For a group of 200 newborn members of the population, approximately how many would be expected to survive the first 3 months of life?
(A) 140
(B) 146
(C) 152
(D) 162
(E) 170
ans:B
the survival rate=9/10, X/200=9/10 => X=180
我算了几遍,都是这个结果,我错在哪里呢?作者: 猫猫头 时间: 2003-3-7 16:37
200*0.9^3作者: joywzy 时间: 2003-3-7 17:06
以下是引用猫猫头在2003-3-7 16:37:03的发言：
200*0.9^3
为什么?作者: 猫猫头 时间: 2003-3-7 17:13
???
200*(1-0.1)survive in the first month
200*(1-0.1)(1-0.1)=survive in the second month
200*(1-0.1)(1-0.1)(1-0.1)=survive in the third month
clear now???作者: xmwangyu 时间: 2003-3-8 12:23
NOTICE "each of the first 3 months "作者: joywzy 时间: 2003-3-8 17:13
谢谢猫猫和xmwangyu！！明白了。作者: 猫猫头 时间: 2003-3-8 20:55
不用谢^_^
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