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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]

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20 Aug 2008, 01:52
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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, 09:25, edited 1 time in total.
Renamed the topic, edited the question and added the OA.

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Re: In a certain animal population, for each of the first 3 mont [#permalink]

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20 Aug 2008, 02:50
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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]

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20 Aug 2008, 04:52
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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: In a certain animal population, for each of the first 3 mont [#permalink]

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20 Aug 2008, 13:50
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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12 Mar 2011, 12:39
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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12 Mar 2011, 12:41
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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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12 Mar 2011, 12:48
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]

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17 Aug 2014, 07:26
Hello from the GMAT Club BumpBot!

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Re: In a certain animal population, for each of the first 3 mont [#permalink]

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31 Oct 2015, 10:58
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]

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01 Nov 2015, 23:00
Bunuel 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, 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.

Hi Bunuel,

If probability of survival can be calculated with 3 times 9/10 , the same can apply to probability of death for 3 months. But the answers would be different.

200*1/10*1/10*1/10 = 0.2.

Can you explain why this approach does not work ?
Thanks.

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Re: In a certain animal population, for each of the first 3 mont [#permalink]

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16 Sep 2016, 07:37
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, 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 critical mistake here is to think that 1/10 per month, 3 months is 3/10 this will yield an answer choice that is a trap - A.
1/10 * 200 = 180 - how many will survive 1st month - we can eliminate A and E.
180 * 1/10 = 162 - how many will survive 2nd month - we can eliminate A, D, and E.
so it's between B and C.
162 = 100%, 16.2 = 10%. 162-16 = 146 aprox. so B.

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Re: In a certain animal population, for each of the first 3 mont   [#permalink] 16 Sep 2016, 07:37
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