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# If a certain set of GMAT test score has a mean of 550 and a standard

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Status: Preparing for GMAT
Joined: 25 Nov 2015
Posts: 983
Location: India
GPA: 3.64
If a certain set of GMAT test score has a mean of 550 and a standard  [#permalink]

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25 Aug 2018, 08:16
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Difficulty:

15% (low)

Question Stats:

94% (00:34) correct 6% (01:42) wrong based on 16 sessions

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If a certain set of GMAT test score has a mean of 550 and a standard deviation of 23, and Rob's score is within two standard deviations from the mean, which of the following CANNOT be Rob's score?
A) 402
B) 543
C) 550
D) 583
E) 590

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Re: If a certain set of GMAT test score has a mean of 550 and a standard  [#permalink]

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25 Aug 2018, 08:39
If you stumbled upon this question and have no clue on how to go about it, go through the basic concepts on Standard Deviation (and Normal Distribution) here and then try solving the question again, this time you should get the right answer without going through the following explaination. Good luck!

Since the mean is 550 and the Standard Deviation is 23 and Rob's score is within 2 Standard Deviations.

550-2(23) < Rob's Score < 550+2(23) [In words, two Standard Deviations span up to 46 on both sides of the mean.]
550-46 < Rob's Score < 550+46
504 < Rob's Score < 596

The answer choice A is the only option not lying in this range, hence it should be the answer.

souvonik2k wrote:
If a certain set of GMAT test score has a mean of 550 and a standard deviation of 23, and Rob's score is within two standard deviations from the mean, which of the following CANNOT be Rob's score?
A) 402
B) 543
C) 550
D) 583
E) 590

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File comment: Normal Distribution (clipped from the awesome GMATClub Math Book)

2018-08-25.png [ 173.43 KiB | Viewed 259 times ]

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Re: If a certain set of GMAT test score has a mean of 550 and a standard  [#permalink]

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25 Aug 2018, 10:13
souvonik2k wrote:
If a certain set of GMAT test score has a mean of 550 and a standard deviation of 23, and Rob's score is within two standard deviations from the mean, which of the following CANNOT be Rob's score?
A) 402
B) 543
C) 550
D) 583
E) 590

$$Given \ Range$$ = $$Mean$$ + $$2SD$$

Or, $$Given \ Range$$ = $$550$$ + $$2*23$$

Or, $$Given \ Range$$ = $$550$$ + $$46$$

So, The Given Range of score must be within $$550 + 46$$ to $$550 - 46$$ , ie between $$504$$ to $$596$$

Among the given options only (A) falls out of the range, hence Answer must be (A)
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Re: If a certain set of GMAT test score has a mean of 550 and a standard &nbs [#permalink] 25 Aug 2018, 10:13
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