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anonymous

  • one year ago

The random variable Y is normally distributed with a mean of 470, and the value Y= 340 is at the 15th percentile of the distribution. Of the following, which is the best estimate of the standard deviation of the distribution? A. 125 B. 135 C. 145 D. 155 E. 165

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  1. anonymous
    • one year ago
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    |dw:1436991107094:dw|

  2. phi
    • one year ago
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    yes, and the 15th percentile is at about -1 std dev

  3. anonymous
    • one year ago
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    k

  4. anonymous
    • one year ago
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    I'm so sorry i have to brb my mom needs help upstairs brb

  5. phi
    • one year ago
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    -1 std deviation means you are one standard deviation less than the mean the mean is 470 and 15th percentile is 340 the difference is about 1 standard deviation

  6. phi
    • one year ago
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    based on the choices, we have to be more accurate. based on your curve, -1 std deviation is at the 16th percentile (2+14= 16) and we are given the 15th percentile = 340 |dw:1436991677454:dw|

  7. phi
    • one year ago
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    the red line at -1 std dev is a little bit closer to the mean... so the difference should be a little bit less than 130

  8. anonymous
    • one year ago
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    Hey so how did you know that it was at the 16th percentile?

  9. anonymous
    • one year ago
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    oh wait nvm i see it now

  10. anonymous
    • one year ago
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    so if it's a little bit less than 130 it's 125?

  11. phi
    • one year ago
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    if you have a z-table, you could look up the z score for 0.15 (I think it's about 1.04) and then say 1.04*s= 130 s= 130/1.04 s= 125

  12. anonymous
    • one year ago
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    hmmm ok i got it thank you !!

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