Anonymous
Anonymous asked in Science & MathematicsMathematics · 2 months ago

need tutor with this question ?

I got 142.8 for first time and then got 132.5 for second time, i use .25=(x-130)/10, what's the wrong part for this question?

Attachment image

7 Answers

Relevance
  • Alan
    Lv 7
    2 months ago
    Favourite answer

    I use .25=(x-130)/10

    You shouldn't use this .  

    First , since this is question about the mean of eight measurements

    The standard deviation = population standard deviation/sqrt(N) 

    so standard deviation = 10/sqrt(8)  not just 10 

    second P(z>Z) =0.1 

    means P(z<Z) = 0.9 

    if you reverse lookup , P(z<approx. 1.2815) = 0.9

    so your starting equation should be

    1.2815  = (x-130) /  (10/sqrt(8)) 

    or if your class allows you to use the closest Z value 

    1.28 = (x-130)/ (10/sqrt(8))  

    start here and see if you come with my answer.   

    P(X_bar > L)  = 1- P(X<L)  

    P(X_Bar>L ) = 0.1 

    0.1 = 1 -P(X_bar<L) 

    P(X<L)  = 1-0.1 =0.9    

    P(z<Z) = 0.9 

    P(z< 1.28) =  0.89973 .

    P(z<  1.29      )  = 0.90147 

    If you interpolate, you get 

    P(z< 1.2815)  =  0.90 

    Z = (L-mean)/ (standard deviation/ sqrt(N))  

    1.2815 = (L-130)/ (10/sqrt(8)) 

    1.2815*10/sqrt(8) = L -130 

    L = 130+ 1.2815*10/sqrt(8) =  134.5307867

    L = 134.53  (if you interpolate) 

    if you take the closest value for Z = 1.28 

    L = 130 + 1.28*10/sqrt(8) =    134.5254834

    which still rounds to 

    L = 134.53  

  • MyRank
    Lv 6
    2 months ago

    1.28 = (x-130) / (10)

    1.28 x 10 = (x-130)

    12.8 = (x-130)

    x = 130 + 12.8 

  • Anonymous
    2 months ago

    Post your work.          

    • Commenter avatarLog in to reply to the answers
  • Anonymous
    2 months ago

    How did you get 142.8? You must have made a mistake.

    • alice2 months agoReport

      yes i totally make a big mistake when i did the second steps

    • Commenter avatarLog in to reply to the answers
  • What do you think of the answers? You can sign in to give your opinion on the answer.
  • 2 months ago

    .25 = (x - 130) / 10

    multiply both sides by 100,

    25 = 10 (x - 130)

    25 = 10 x - 1300

    10 x = 25 + 1300

    10 x = 1325

    x = 132.5

    • ...Show all comments
    • Alan
      Lv 7
      2 months agoReport

      no you said 8 measurements  
      population standard deviation/sqrt(N) = 10/ sqrt(8)  

    • Commenter avatarLog in to reply to the answers
  • 2 months ago

    multiply both sides by 10

    2.5 = x - 130

    add 130 to both sides

    132.5 = x

    • ...Show all comments
    • Alan
      Lv 7
      2 months agoReport

      Try solving
      1.2816 = (x-130)/ (10 /sqrt(8) )
      for x
      since that is the correct equation. 

    • Commenter avatarLog in to reply to the answers
  • 2 months ago

    Remember the order of operations. Look for it in your textbook. I'm not doing your homework for you.

    • Commenter avatarLog in to reply to the answers
Still have questions? Get answers by asking now.