A scientist recorded the number of eggs in each of 10 birds'

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A scientist recorded the number of eggs in each of 10 birds' [#permalink]

11 Sep 2012, 04:50

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The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions Project

A scientist recorded the number of eggs in each of 10 birds' nests. What was the standard deviation of the numbers of eggs in the 10 nests?

(1) The average (arithmetic mean) number of eggs for the 10 nests was 4.
(2) Each of the 10 nests contained the same number of eggs.

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Re: A scientist recorded the number of eggs in each of 10 birds' [#permalink]

11 Sep 2012, 04:50

SOLUTION

A scientist recorded the number of eggs in each of 10 birds' nests. What was the standard deviation of the numbers of eggs in the 10 nests?

The standard deviation of a set is always more than or equal to zero (SD\geq{0}). The standard deviation is 0 only when a set contains all identical elements (or which is same only 1 element).

(1) The average (arithmetic mean) number of eggs for the 10 nests was 4. Knowing the average does not help to get the standard deviation. Not sufficient.

(2) Each of the 10 nests contained the same number of eggs. So, the set contains all identical elements, which means that the standard deviation is zero. Sufficient.

Answer: B.
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Re: A scientist recorded the number of eggs in each of 10 birds' [#permalink]

11 Sep 2012, 08:13

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scientist recorded the number of eggs in each of 10 birds' nests. What was the standard deviation of the numbers of eggs in the 10 nests?

(1) The average (arithmetic mean) number of eggs for the 10 nests was 4.
(2) Each of the 10 nests contained the same number of eggs.

SD = Sqrt( sum(x-Mean)^2/n)

1 is INEFF as we can take two samples, sample one 5 nests were 3 and 5 nests were 5 - arithmetic means = 4.
another sample, 5 nests are 2 and 5 nests are 6, arithmetic mean 4 again but standard deviation (the dispersion of data points) is larger

2 is GOOD as the SD = 0, if all the same, no dispersion,

Answer is B
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Re: A scientist recorded the number of eggs in each of 10 birds' [#permalink]

12 Sep 2012, 04:02

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Bunuel wrote:

A scientist recorded the number of eggs in each of 10 birds' nests. What was the standard deviation of the numbers of eggs in the 10 nests?

(1) The average (arithmetic mean) number of eggs for the 10 nests was 4.
(2) Each of the 10 nests contained the same number of eggs.

St 1: Insufficient: Avg no of eggs for 10 nest is 4. ie total no of eggs are 40. So we can distribute it in 10 nests in various combinations. Hence the SD will vary accordingly.
St 2: Sufficient: Since each nest contains same no of eggs the SD is "0"

Hence Answer is B
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Re: A scientist recorded the number of eggs in each of 10 birds' [#permalink]

12 Sep 2012, 13:20

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The question can be simplified to " What is distribution of Eggs in 10 nests from the mean no of eggs"

Statement 1- Mean is given but no information is given regarding the distribution around mean.------> Insufficient.
Statement 2- As each nest contain the same no of eggs, there is '0' distribution around mean.------>Sufficient.

Answer B

Hope it helps
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Re: A scientist recorded the number of eggs in each of 10 birds' [#permalink]

14 Sep 2012, 06:31

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standard deviation [#permalink]

23 Jan 2013, 08:29

A scientist recorded the number of eggs in each of 10 bird's nests.
What was the standard deviation of the numbers of eggs in the 10 nests?

(1) The average(arithmetic mean) number of eggs for the 10 nests was 4.
(2) Each of the 10 nests contained the same number of eggs.
-------------------------------------------------------------------------------------------

This question does not make sense to me.
Isn't the question self-sufficient?
The scientist recorded the number of eggs in each of 10 nests.
so he/she can calculate the average and standard deviation as well.
Why does he/she need (1) or (2) ?

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Re: standard deviation [#permalink]

23 Jan 2013, 08:35

slifedt wrote:

Merging similar topics. Pleas refer to the solutions above.

As for your doubt, the statements are sufficient if WE can calculate SD based on the info given not the scientist.

P.S. Please read carefully and follow: rules-for-posting-please-read-this-before-posting-133935.html Pay attention to the rule #3: the name of a topic (subject field) MUST be the first 40 characters (~the first two sentences) of the question.
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Re: A scientist recorded the number of eggs in each of 10 birds' [#permalink]

24 Jan 2013, 13:19

Statement 1: We know the mean but we don't have any other information to compute the SD. Insufficient.
Statement 2: If all the nests contain the same amount of eggs, the mean # of eggs would be the same as # eggs in every nest...no matter how many eggs there are the SD will always be 0. Sufficent.

Re: A scientist recorded the number of eggs in each of 10 birds' [#permalink] 24 Jan 2013, 13:19

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A scientist recorded the number of eggs in each of 10 birds'

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A scientist recorded the number of eggs in each of 10 birds'

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