Quantcast

Got Homework?

Connect with other students for help. It's a free community.

  • across
    MIT Grad Student
    Online now
  • laura*
    Helped 1,000 students
    Online now
  • Hero
    College Math Guru
    Online now

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

order

the lengths in cm of drinking straws produced in a factory have a normal distribution with mean mu and variance 0.64. it is given that 10% of the straws are shorter than 20cm (i) find the value of mu. It says you first find the s.d. which is sqrt:0.64 which is 0.8. then with the formula you place \[ 20- mu \over 0.8\].Then it says <10% or >90%. The mark scheme uses z>90% so it ends up as (p) = -1.282 according to the normal distribution chart. So, you equate that formula to that, but why can't it be <10%?

  • one year ago
  • one year ago

  • This Question is Closed
  1. kropot72
    Best Response
    You've already chosen the best response.
    Medals 1

    To use <10% you need a -z z table|dw:1337763325038:dw|

    • one year ago
  2. order
    Best Response
    You've already chosen the best response.
    Medals 0

    This doesn't help...

    • one year ago
  3. kropot72
    Best Response
    You've already chosen the best response.
    Medals 1

    z = -1.282\[-1.282=\frac{20-\mu}{0.8}\] \[-1.0256=20-\mu\] \[\mu=21.0256cm\]

    • one year ago
  4. order
    Best Response
    You've already chosen the best response.
    Medals 0

    \[0.1<{20- mu \over 0.8}\] Why can't you use?

    • one year ago
  5. kropot72
    Best Response
    You've already chosen the best response.
    Medals 1

    \[z \neq0.1\] The z-value is the standardised value of a random variable. If you look at the -z z table (which has negative values of z), you would find the z-value of -1.282 leads you to p = 0.1

    • one year ago
  6. order
    Best Response
    You've already chosen the best response.
    Medals 0

    Ok, It's true. Thanks :) I realized my mistake.

    • one year ago
  7. kropot72
    Best Response
    You've already chosen the best response.
    Medals 1

    You're welcome :)

    • one year ago
    • Attachments:

See more questions >>>

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.