Quantcast Probability/Stats Questions? - XP Math - Forums
XP Math Home Sign Up FREE! | Sign In | Classroom Setup | Common Core Alignment PDF Version

Go Back   XP Math - Forums > Welcome > Off-Topic Discussion

Reply
 
Thread Tools Display Modes
Old 07-28-2007   #1
schottr@sbcglobal.net
Guest
 
Posts: n/a
Default Probability/Stats Questions?

Can someone please help me solve the following questions?Scores on a test are normally distributed with a mean of 550 and a standard deviation of 80. a) If one subject is randomly selected, find the probability that the score is between 550 and 650. b) If a job requires a score in the top 80%, find the lowest acceptable score. C) If 50 subjects are randomly selected, find the probability that their mean is between 550 and 650.Thanks!!!
  Reply With Quote
Old 07-28-2007   #2
cubsmtdew
Guest
 
Posts: n/a
Default

How's it going.a) the dif. between 650and 550 is 100. a standard dev. = 80.so we will have 34% + 13.5(.25)%= 3.375 + 34= 37.375%answer to a is 37.375%b)idkc)37.375%*50= 18.675=19 people
  Reply With Quote
Old 07-28-2007   #3
Hobart
Guest
 
Posts: n/a
Default

a) To find the probability of a variable, X, between two limits, a and b when the variable is normally distributed:P(a < X < b) = Φ[(b-µ)/σ] - Φ[(a-µ)/σ] where the values within the square brackets are standard normal z-values. Phi (Φ) is and operator that means "find the probability associated with the Z-values in the square brackets". So evaluating:P(550 < X < 650) = Φ[(650-550)/80] - Φ[(550-550)/80] P(550 < X < 650) = Φ[(650-550)/80] = Φ[1.25] - Φ[0] = 0.8944 - 0.50 = 0.3944b) You want to eliminate the bottom 20%. So the Z-value associated with the BOTTOM 20% is -0.84, and the limit for the bottom 20% is found by:-0.84 = (x - 550)/80; solving for x = 482.8. If an integer is required, then the lowest acceptable score would be 483.c) Find the probability that the sample mean is less than 650:Z = (650-550)/(80/√50) = 100/35.78) = 2.79Then Φ[2.79] - Φ[0] = 0.9974 -0.50 = 0.4974
  Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 03:40 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
XP Math