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# The heights of a certain plant species are normally distributed. What

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Math Expert
Joined: 02 Sep 2009
Posts: 52230
The heights of a certain plant species are normally distributed. What  [#permalink]

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13 Apr 2018, 00:40
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Difficulty:

35% (medium)

Question Stats:

68% (00:34) correct 32% (01:15) wrong based on 49 sessions

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The heights of a certain plant species are normally distributed. What height is 2 standard deviations greater than the arithmetic mean height of the plant species?

(1) The arithmetic mean height is 32.8 centimeters.
(2) The standard deviation of the heights is 2.4 centimeters.

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Joined: 28 Apr 2014
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GMAT 1: 640 Q50 V25
Re: The heights of a certain plant species are normally distributed. What  [#permalink]

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13 Apr 2018, 00:43
1
IMO A

St1 sd =32.8+2=34.8
St2 can't get the exact value of sd
Intern
Joined: 29 Aug 2016
Posts: 35
Re: The heights of a certain plant species are normally distributed. What  [#permalink]

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14 Apr 2018, 20:41
E

St 1 gives us the mean. Insufficient.
St 2 tells us the SD value. Insufficient.

St1+St2 gives us the minimum possible value for this question. 32.8+2.4+2.4.
But again, this will be a whole range in the distribution and we cannot give just 1 value for this question.
Insufficient.

I guess this is how it goes.

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Re: The heights of a certain plant species are normally distributed. What  [#permalink]

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15 Apr 2018, 09:49
Bunuel wrote:
The heights of a certain plant species are normally distributed. What height is 2 standard deviations greater than the arithmetic mean height of the plant species?

(1) The arithmetic mean height is 32.8 centimeters.
(2) The standard deviation of the heights is 2.4 centimeters.

If mean is 'x' and if standard deviation is 'y', then value which is one SD greater than mean = x + y, value which is two SD greater than mean = x + 2y, value which is three SD greater than mean = x + 3y.. and so on.
Similarly, value which is one SD lesser than mean = x - y, value which is two SD lesser than mean = x - 2y.. and so on.

Here we need x + 2y. Statement 1 gives us x, while Statement 2 gives us y. So answer should be C.
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Joined: 08 Feb 2018
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The heights of a certain plant species are normally distributed. What  [#permalink]

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17 Apr 2018, 20:15
Why is there always a wide range of answer selections by participants?

How to know which is the correct answer?

Akshay
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And yeah, definitely aim for a level of accuracy where managing time will not be a burden anymore.

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Re: The heights of a certain plant species are normally distributed. What  [#permalink]

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17 Apr 2018, 21:22
akshaykotha wrote:
Why is there always a wide range of answer selections by participants?

How to know which is the correct answer?

Akshay

Answer can be only one out of A, B, C, D, E. As per the question, answer will be revealed on Friday 20th April.

When there is a wide range of answer selections, it means not everyone is able to determine the answer to the question. So I suggest you wait till 20th April when the answer will be revealed and then come back to this question to check those answer explanations which match with the right answer.
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Re: The heights of a certain plant species are normally distributed. What  [#permalink]

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27 Apr 2018, 22:18
As per question
Mean +2*standard deviation

We need both statements to calculate

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Re: The heights of a certain plant species are normally distributed. What &nbs [#permalink] 27 Apr 2018, 22:18
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