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K.Binks

  • one year ago

How do I do problems like this? " The time required to finish a test is normally distributed with a mean of 60 minutes and a standard deviation of 10 minutes. What is the probability a student will finish the test between 50 and 60 minutes?"

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  1. anonymous
    • one year ago
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    You can use the standard normal distribution curve. let me see if I can find one

  2. anonymous
    • one year ago
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    from http://www.oswego.edu/~srp/stats/6895997.htm |dw:1439294802648:dw|

  3. anonymous
    • one year ago
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    Your mean is 60 and standard deviation is 10. So 60 goes in the middle and add 10 to the right, subtract 10 to the left. 34% lies between 50 and 60 |dw:1439294942539:dw|

  4. K.Binks
    • one year ago
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    What about the next one, where the times are 40 and 70?

  5. anonymous
    • one year ago
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    between 40 and 70, add up the percentages between those numbers

  6. anonymous
    • one year ago
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    You can do it the way @shabbaranks is as well and use z-scores. That method works for all possible values. Using the curve only works when the numbers are multiples of the standard deviation

  7. K.Binks
    • one year ago
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    Ok, just add them up, as in 34+34+13.5? I think I understand what you're saying, for both methods. I didn't know what a z-score was, but I think I get it now.

  8. anonymous
    • one year ago
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    Yes that's what I meant. That's right

  9. anonymous
    • one year ago
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    I don't think they make them memorize the chart (hopefully lol) Here's one btw: http://www.regentsprep.org/regents/math/algtrig/ats7/zchart.htm

  10. K.Binks
    • one year ago
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    Ok, I think I got it now. Thank ya'll!

  11. mathmate
    • one year ago
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    @k.binks @peachpi 's method explains visually how the Z-score works, while @shabbaranks 's method gives the procedure to calculate practical problems. You're lucky to have both!

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