 My Math Forum need help with a statistics probability problem
 User Name Remember Me? Password

 Probability and Statistics Basic Probability and Statistics Math Forum

 November 13th, 2007, 10:45 PM #1 Newbie   Joined: Nov 2007 Posts: 2 Thanks: 0 need help with a statistics probability problem I am looking at a sample of an infinite population of manufactured parts. The population is a normal distribution (whatever that means in this case, since I don't know the standard deviation) and 5% of the parts are known to be defective. Now my question: 5% of the manufactured parts of the infinite population are defective. Calculate the probability that the sample of 400 parts contains 36 or more defective parts. How do I do this? November 14th, 2007, 04:37 AM #2 Global Moderator   Joined: Nov 2006 From: UTC -5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms You could do it combinatorially. The chance that exactly n parts out of 400 are defective is .95^(400-n) * .05^n * (400 choose n), then sum this formula from 0 to 35 and subtract from 1. This is a use of the binomial formula, though it requires big numbers: 400 choose 35 is 24685184473786479717864752464078290163400663996640 0. But you were asked to use the normal distribution, which is a great approximation for the binomial distribution at large numbers. The mean is easy to find, and the standard deviation for a binomial distribution is sqrt(np(1-p)) = sqrt(400 * 0.05 * 0.95). So use a z-table with those parameters. November 14th, 2007, 02:07 PM #3 Newbie   Joined: Nov 2007 Posts: 2 Thanks: 0 You know, I think I posted this is the wrong section, because this is a college level statistics course and I have been dealing with sampling distributions of sample means and t-scores and the like. I think I'm supposed to use some of that stuff. November 14th, 2007, 06:17 PM   #4
Global Moderator

Joined: Nov 2006
From: UTC -5

Posts: 16,046
Thanks: 938

Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms
Quote:
 Originally Posted by euromath You know, I think I posted this is the wrong section, because this is a college level statistics course and I have been dealing with sampling distributions of sample means and t-scores and the like. I think I'm supposed to use some of that stuff.
Yeah, probably. Of course if it looked like a high school problem I probably wouldn't have answered it.  Tags probability, problem, statistics Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post Mighty Mouse Jr Probability and Statistics 2 February 4th, 2013 07:23 AM Deeper Advanced Statistics 12 September 11th, 2011 10:42 AM MasterOfDisaster Probability and Statistics 4 August 11th, 2011 10:49 PM kylerwoods Probability and Statistics 1 May 21st, 2010 04:34 AM katielangford1 Advanced Statistics 0 December 31st, 1969 04:00 PM

 Contact - Home - Forums - Cryptocurrency Forum - Top      