# 09_23_09ans - STAT 409 1 Fall 2009 Examples for A machine...

This preview shows pages 1–2. Sign up to view the full content.

STAT 409 Examples for 09/23/2009 Fall 2009 1. A machine makes ½-inch ball bearings. In a random sample of 41 bearings, the sample standard deviation of the diameters of the bearings was 0.02 inch. Assume that the diameters of the bearings are approximately normally distributed. Construct a 90% confidence interval for the standard deviation of the diameters of the bearings. s = 0.02. n = 41. The confidence interval : ( 29 ( 29 - - - 1 , 1 2 2 1 2 2 2 2 α α χ s χ s n n . 90% confidence level α = 0.10 α 2 = 0.05 . n – 1 = 40 degrees of freedom. 2 05 0 2 2 . χ χ = α = 55.76 . 2 95 0 2 2 1 . χ χ = α - = 26.51 . ( 29 ( 29 - - 51 . 26 02 . 0 1 41 , 76 . 55 02 . 0 1 41 2 2 ( 0.01694 , 0.02457 ) 2. The service time in queues should not have a large variance; otherwise, the queue tends to build up. A bank regularly checks service time by its tellers to determine its variance. A random sample of 22 service times (in minutes) gives

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 10/12/2011 for the course STATISTICS stat 410 taught by Professor Stepanov during the Spring '11 term at University of Illinois, Urbana Champaign.

### Page1 / 2

09_23_09ans - STAT 409 1 Fall 2009 Examples for A machine...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online