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freezer · 2007 September 5th, 02:49 AM

For a certain exam a score of 58 is 2 standard deviations below the mean and a score of 98 is 3 standard deviations above mean. What was the mean score of the exam?

a) 16
b) 40
c) 72
d) 74
82

Could anyone give me step by step solution?

Thanks

krishna_k1 · 2007 September 5th, 05:26 AM

Answer is d.

74 - 58 = 16. so the sd is 8. 8 *3 + 74 = 98.

aru4912 · 2007 September 9th, 06:42 PM

M=> mean, S.D=> Standard Deviation

M-58 = 2 * S.D
M+3 * SD =98

Rearranging ..,
M-58=2SD
M-98 = -3SD

=> 5 SD = 40 => SD = 5

Subst. SD in anyone of the above eqn. will give you the mean.It is 74

bhavinparekh · 2007 September 10th, 08:33 PM

D.

The way I figured it out was to take the difference between 58 & 98
98 - 58 = 40. This corresponds to 5 standard deviations for the question.

Hence, 40/5 = 8 is one standard deviation....

So Mean = 58 + 2*8 = 74; 98 - 3*8 = 74.

Hence D.

CrackXam · 2007 September 12th, 03:49 PM

Can someone por favor, El Señor list the formulae for standard deviation!

Thanks

Prawler · 2007 September 12th, 11:47 PM

[Sum (Variable - Mean ) ] / n

n= number of variables.

krusta80 · 2007 September 13th, 01:01 AM

Quote:

Originally Posted by Prawler

[Sum (Variable - Mean ) ] / n

n= number of variables.

Not correct.

std dev = sqrt(Sum([Variable-Mean]^2)/n)

Giscard · 2007 September 13th, 08:50 PM

You don't need to know std dev to solve this problem. 58 is 2*stuff down, 98 is 3*stuff up. Whatever this "stuff" might be, the answer is 74.

bads123 · 2007 September 24th, 04:09 AM

avg = 58 + 2d
avg = 98 - 3d
d = 8
avg = 74

umgrad76 · 2007 September 25th, 05:42 AM

I agree 98-85 = 40 ---> 40/5=8 ----> 58+2*8=74

2007 September 5th, 02:49 AM	#1 (permalink)
freezer Eager! Join Date: Sep 2007 Posts: 80	Standard Deviation Problems 2 For a certain exam a score of 58 is 2 standard deviations below the mean and a score of 98 is 3 standard deviations above mean. What was the mean score of the exam? a) 16 b) 40 c) 72 d) 74 82 Could anyone give me step by step solution? Thanks

2007 September 12th, 03:49 PM	#5 (permalink)
CrackXam TestMagic Guru-in-Training Join Date: Jun 2007 Location: Gurgaon, India Posts: 740	Can someone por favor, El Señor list the formulae for standard deviation! Thanks _ _ _ _ SIG _ _ _ _ Success is achieved not by strength, but perseverance! (Abridged) - Samuel Johnson

2007 September 13th, 08:50 PM	#8 (permalink)
Giscard Within my grasp! Join Date: Oct 2004 Location: Lincoln, Nebraska Posts: 103	You don't need to know std dev to solve this problem. 58 is 2stuff down, 98 is 3stuff up. Whatever this "stuff" might be, the answer is 74. _ _ _ _ SIG _ _ _ _ Stranger in a strage land

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2007 September 5th, 05:26 AM	#2 (permalink)
krishna_k1 Eager! Join Date: Aug 2007 Posts: 63	Answer is d. 74 - 58 = 16. so the sd is 8. 8 *3 + 74 = 98.

2007 September 9th, 06:42 PM	#3 (permalink)
aru4912 TestMagic Guru-in-Training Join Date: Jun 2006 Location: New York Posts: 724	M=> mean, S.D=> Standard Deviation M-58 = 2 * S.D M+3 * SD =98 Rearranging .., M-58=2SD M-98 = -3SD => 5 SD = 40 => SD = 5 Subst. SD in anyone of the above eqn. will give you the mean.It is 74

2007 September 10th, 08:33 PM	#4 (permalink)
bhavinparekh I JUST got here. Join Date: Jun 2006 Posts: 9	D. The way I figured it out was to take the difference between 58 & 98 98 - 58 = 40. This corresponds to 5 standard deviations for the question. Hence, 40/5 = 8 is one standard deviation.... So Mean = 58 + 28 = 74; 98 - 38 = 74. Hence D.

2007 September 12th, 11:47 PM	#6 (permalink)
Prawler Within my grasp! Join Date: Jul 2007 Posts: 354	[Sum (Variable - Mean ) ] / n n= number of variables.

2007 September 24th, 04:09 AM	#9 (permalink)
bads123 Learning never Stops ! Join Date: Aug 2007 Posts: 122	avg = 58 + 2d avg = 98 - 3d d = 8 avg = 74

2007 September 25th, 05:42 AM	#10 (permalink)
umgrad76 Eager! Join Date: Sep 2007 Posts: 64	I agree 98-85 = 40 ---> 40/5=8 ----> 58+2*8=74

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