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Thread: Standard Deviation Problems 2

  1. #1
    Eager! freezer just joined TestMagic.
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    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

  2. #2
    Eager! krishna_k1 just joined TestMagic.
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    Answer is d.

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

  3. #3
    TestMagic Guru-in-Training aru4912 is on the way!
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    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

  4. #4
    Trying to make mom and pop proud bhavinparekh just joined TestMagic. bhavinparekh's Avatar
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    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.

  5. #5
    TestMagic Guru-in-Training CrackXam is on the way!
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    Can someone plz list the formulae for standard deviation!

    Thanks
    Success is achieved not by strength, but perseverance! (Abridged) - Samuel Johnson

  6. #6
    Within my grasp! Prawler just joined TestMagic.
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    [Sum (Variable - Mean ) ] / n

    n= number of variables.

  7. #7
    TestMagic Guru-in-Training krusta80 's dreams are becoming reality.
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    Quote Originally Posted by Prawler View Post
    [Sum (Variable - Mean ) ] / n

    n= number of variables.
    Not correct.

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

  8. #8
    Within my grasp! Giscard just joined TestMagic. Giscard's Avatar
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    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.
    Stranger in a strage land

  9. #9
    Learning never Stops ! bads123 just joined TestMagic.
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    avg = 58 + 2d
    avg = 98 - 3d
    d = 8
    avg = 74

  10. #10
    Eager! umgrad76 just joined TestMagic.
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    I agree 98-85 = 40 ---> 40/5=8 ----> 58+2*8=74

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