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# In a certain animal population for each of the first 3

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Intern
Joined: 20 Jul 2008
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In a certain animal population for each of the first 3 [#permalink]  20 Aug 2008, 00:52
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Difficulty:

5% (low)

Question Stats:

100% (02:12) correct 0% (00:00) wrong based on 1 sessions
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, aprroximately how many would be expected to survive the first 3 month of life?
a)140
b)146
c)152
d)162
e)170

How would you solve this? Thanks
Intern
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Re: PS Probabilty Question: in a certain animal population [#permalink]  20 Aug 2008, 01:50
My take,
P(animal dying during first 3 months) = P(dying in M1) + P(dying in M2) + P(dying in M3)
= (1/10) + (9/10)*(1/10) + (9/10)*(9/10)*(1/10)
= 271/1000

P(animal surviving the first 3 months) = 729/1000

No Of animals surviving (approx) = (729/1000) * 200 = 146

What is the OA?
Director
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Re: PS Probabilty Question: in a certain animal population [#permalink]  20 Aug 2008, 03:52
Ginc wrote:
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, aprroximately how many would be expected to survive the first 3 month of life?
a)140
b)146
c)152
d)162
e)170

How would you solve this? Thanks

Number of newborns that can die in first month = 1/10 * 200 = 20

Survived = 180

Number of newborns that can die in second month = 1/10 * 180 = 18

Survived = 162

Number of newborns that can die in third month = 1/10 * 162 = 16

Survived = 146
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Re: PS Probabilty Question: in a certain animal population [#permalink]  20 Aug 2008, 05:39
Having a look at the replies now, thanks OA is 146
Manager
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Re: PS Probabilty Question: in a certain animal population [#permalink]  20 Aug 2008, 12:50
200 * .10 = 20 died

180 * .10= 18 died

162 * .10= 16.2 = 16 died

Total died = 54

200-54= 146 (B)
Re: PS Probabilty Question: in a certain animal population   [#permalink] 20 Aug 2008, 12:50
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