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anonymous

  • one year ago

the life expectancy of a typical light bulb is normally distributed with a mean of 2000 hours and a standard deviaton of 27 hours. what is the probability that a lightbulb will last between 1975 and 2050 hours? a.)0.17619 b.)0.32381 c.)0.79165 d.)0.96784

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  1. Vocaloid
    • one year ago
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    convert 1975 and 2050 to z-scores using the formula z-score = (given number - mean)/standard deviation then use a z-table or a calculator (normalcdf(z-score1,z-score2) to find the probability

  2. anonymous
    • one year ago
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    Idk what that is

  3. anonymous
    • one year ago
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    A z-table I mean

  4. Vocaloid
    • one year ago
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    http://4.bp.blogspot.com/_5u1UHojRiJk/TEh9BHxxPUI/AAAAAAAAAIQ/DafeQNMYFoE/s1600/ztable.gif

  5. anonymous
    • one year ago
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    Okay.. how would I find the z-scores?

  6. Vocaloid
    • one year ago
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    use the formula I just gave you

  7. anonymous
    • one year ago
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    Would the answer be 0.96784

  8. Vocaloid
    • one year ago
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    hm, not quite, can you tell me where you got your answer?

  9. anonymous
    • one year ago
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    I'm a little confused on how to do this all. The two answers I got were -.925925926 and 1.851851852

  10. Vocaloid
    • one year ago
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    your numbers are right, you're just not done yet 1. find the probability that corresponds to -.925925926 using the z-table 2. find the probability that corresponds to 1.851851852 using the z-table take the result from part 2 and subtract the result from part 1

  11. anonymous
    • one year ago
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    I got .925925926

  12. Vocaloid
    • one year ago
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    uh, not quite use the z-table to find the probability that corresponds to -.925925926

  13. Vocaloid
    • one year ago
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    actually, do you have a graphing calculator with you?

  14. anonymous
    • one year ago
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    No I don't

  15. Vocaloid
    • one year ago
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    alright, so for the z-score -.925925926 we're going to round to -0.93, and use this z-table to find the probability https://www.bing.com/images/search?q=negative+z+table&view=detailv2&&&id=0EE0897D340872D7DD333EA703C06E1FAFE3D682&selectedIndex=0&ccid=UAu%2f5RDN&simid=608005827397226440&thid=JN.QiHVxQ5sExJprxixifrppg&ajaxhist=0 look at the left column and find the row -0.9, then go across to the column 0.03 and tell me what number is in the box

  16. Vocaloid
    • one year ago
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    |dw:1433555811431:dw|

  17. anonymous
    • one year ago
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    .1762 so it's the first answer. Thank you :)

  18. anonymous
    • one year ago
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    It was C.

  19. Vocaloid
    • one year ago
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    ahh sorry for the late reply you're supposed to do the same thing we just did for 1.851851852 and subtract the two values

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