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

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

35% (medium)

Question Stats:

66% (02:25) correct 34% (01:03) wrong based on 68 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, approximately how many would be expected to survive the first 3 months of life?

A. 140
B. 146
C. 152
D. 162
E. 170
[Reveal] Spoiler: OA

Last edited by Bunuel on 17 Aug 2014, 08:25, edited 1 time in total.
Renamed the topic, edited the question and added the OA.
Intern
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Re: In a certain animal population, for each of the first 3 mont [#permalink]  20 Aug 2008, 01:50
1
KUDOS
1
This post was
BOOKMARKED
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?
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Re: In a certain animal population, for each of the first 3 mont [#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
Manager
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Re: In a certain animal population, for each of the first 3 mont [#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)
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Re: Animal population [#permalink]  12 Mar 2011, 11:39
200/10=20 will die in the first month.
Left 180
180/10=18 will die in the 2nd
Left 162
162/10=16.2=16 will die in the 3rd

Total dead = 20+18+16 = 54
Alive = 200-54= 146

Ans: "B"
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Re: Animal population [#permalink]  12 Mar 2011, 11:41
Expert's post
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

The probability of survival for each of the first 3 months of life is 1-1/10=9/10, so of 200 newborn 200*9/10*9/10*9/10=~146 is expected to survive.

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Re: Animal population [#permalink]  12 Mar 2011, 11:48
Good question.

Its important to see the given death probability is for one month, otherwise one can get this wrong.
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Re: In a certain animal population, for each of the first 3 mont [#permalink]  17 Aug 2014, 06:26
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: In a certain animal population, for each of the first 3 mont   [#permalink] 17 Aug 2014, 06:26
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