# Confidence Interval of percentage of rivets

Not what you're looking for?

4.) 20 rivets out 100 in a new box that we tested had break strength below the desired level. Since this is a critical part for assembly, we want to be 99% confident of how many rivets are below the desired level. Calculate the confidence interval of the percentage of rivets that are below the desired level.

5.) We expect a 1.5% response/mail rate in a particular mail campaign. We are going to test a new outer envelope with the phrase "Open me first". We would like to be accurate within 0.25% (0.0025) of the true response/mail rate for future mailings. How many mail pieces should we mail and how confident would you want to be?

6.) Write your own simple problem using the concept of Expected Value and solve.

##### Purchase this Solution

##### Solution Summary

4.) 20 rivets out 100 in a new box that we tested had break strength below the desired level. Since this is a critical part for assembly, we want to be 99% confident of how many rivets are below the desired level. Calculate the confidence interval of the percentage of rivets that are below the desired level.

5.) We expect a 1.5% response/mail rate in a particular mail campaign. We are going to test a new outer envelope with the phrase "Open me first". We would like to be accurate within 0.25% (0.0025) of the true response/mail rate for future mailings. How many mail pieces should we mail and how confident would you want to be?

6.) Write your own simple problem using the concept of Expected Value and solve.

##### Solution Preview

4) Applying the general formula for a confidence interval, the confidence interval for a proportion, p, is: p+- z*Sp

<br>where p is the proportion in the sample, z depends on the level of confidence desired, and Sp, the standard error of a proportion, is equal to: Sp=SQRT(p(1-p)/n)

<br>In this case, p=20/100=0.2, Sp=SQRT(0.2(1-0.2)/100)=0.04

<br>Since it's a two-tailed distribution, we should use the 0.995 level of confidence. (0.005 on each side), from the z-table, we can find z=2.58

<br>So upper limit is: ...

##### Purchase this Solution

##### Free BrainMass Quizzes

##### Measures of Central Tendency

This quiz evaluates the students understanding of the measures of central tendency seen in statistics. This quiz is specifically designed to incorporate the measures of central tendency as they relate to psychological research.

##### Measures of Central Tendency

Tests knowledge of the three main measures of central tendency, including some simple calculation questions.

##### Know Your Statistical Concepts

Each question is a choice-summary multiple choice question that presents you with a statistical concept and then 4 numbered statements. You must decide which (if any) of the numbered statements is/are true as they relate to the statistical concept.

##### Terms and Definitions for Statistics

This quiz covers basic terms and definitions of statistics.