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yashar806

  • 3 years ago

Weights of apples grown in an orchard are known to follow a normal distribution with mean 160 grams. It is known that approximately 99.7% of apples have weights between124 and 196 grams. What is the standard deviation of weights of all apples grown in the orchard?

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  1. tomo
    • 3 years ago
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    |dw:1363376606947:dw|

  2. yashar806
    • 3 years ago
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    but i cant get the right answer

  3. yashar806
    • 3 years ago
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    i used that that formula

  4. tomo
    • 3 years ago
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    |dw:1363376747863:dw|

  5. tomo
    • 3 years ago
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    z1 = (124-160)/sigma z2 = (196-160)/sigma 1-z1-z2 = (99.7)/100

  6. tomo
    • 3 years ago
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    i have to leave, but I think that should help you find the answer

  7. amistre64
    • 3 years ago
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    dont we just need one of those to determine sigma?

  8. amistre64
    • 3 years ago
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    \[z=\frac{x-\bar x}{sd}\] \[sd=\frac{x-\bar x}{z}\]

  9. yashar806
    • 3 years ago
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    i got confused

  10. yashar806
    • 3 years ago
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    why we need to 1- them

  11. amistre64
    • 3 years ago
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    or rather, we dont have the z value explicitly do we

  12. yashar806
    • 3 years ago
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    we do have z

  13. yashar806
    • 3 years ago
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    99.7%

  14. amistre64
    • 3 years ago
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    |dw:1363377005023:dw|

  15. amistre64
    • 3 years ago
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    we have an implicit z, we can either use the zscore of .3/2 .. or 99.7+.3/2

  16. yashar806
    • 3 years ago
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    what would be answer?

  17. amistre64
    • 3 years ago
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    does that make sense? 99.7% is inbetween those values, so the proper zscore has to be adjusted. use z(.9985), at x=196 or, z(.0015), at x=124

  18. yashar806
    • 3 years ago
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    yes

  19. amistre64
    • 3 years ago
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    id prolly use the 196 version

  20. amistre64
    • 3 years ago
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    can you tell me the zscore of .9985?

  21. yashar806
    • 3 years ago
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    2.96

  22. amistre64
    • 3 years ago
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    i agree soo, sd= (196-160)/2.96

  23. yashar806
    • 3 years ago
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    oh, i got it

  24. yashar806
    • 3 years ago
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    can we use both of them?

  25. amistre64
    • 3 years ago
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    both of what?

  26. yashar806
    • 3 years ago
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    z1 = (124-160)/sigma z2 = (196-160)/sigma

  27. yashar806
    • 3 years ago
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    like that

  28. amistre64
    • 3 years ago
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    we can, the sd will be negative for the z1 equation and the percentage at z1 is (.0015), iinstead of (.9985)

  29. yashar806
    • 3 years ago
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    thats wht i used initially

  30. yashar806
    • 3 years ago
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    but i got wrong answer

  31. amistre64
    • 3 years ago
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    one chk would be to do (124-160)/12.1622 and see if its about -.0015 :)

  32. amistre64
    • 3 years ago
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    hmm, i get -2.96 is 160 by chance the average of 124 and 196?

  33. amistre64
    • 3 years ago
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    .... yep

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