# It seems me true but?

1. Oct 3, 2009

### kristymassi

it seems me true but prof. said its not..

You are asked to calculate the probability that a sample of 1000 vaccine vials from a filling line contains no more than two (2) defective closures. From prior data, you know that the particular filling line in question has a defect rate of 0.08%. Given this information, you use the Microsoft Excel BINOMDIST function with number_s =2, trials = 1000, and probability_s = 0.0008. In order to yield the desired probability, you should set the value of cumulative = TRUE and subtract the result of the function from 1.000.

is that true?

2. Oct 3, 2009

### SW VandeCarr

You gave an observed rate of 8 defects per 1000 but no variance. If you can assume a Poisson process then the mean and variance is 8 and the SD=sqrt (8). From this you can estimate the probability of 2 defects per thousand.

EDIT: I'm confused about your denominator. Is it 1000 or 10000? In either case the above works as long as your denominator doesn't change. You can also use a chi- square estimate where E=8, O=2 and Chi sq=(E-O)^2/E. You can get the probability from Chi Square tables.

Last edited: Oct 3, 2009
3. Oct 3, 2009

### kristymassi

SW VandeCarr, thank you very much

When we set the value of cumulative to TRUE, we already getthe probability of 2 or less
than 2 (that is no more than 2) defectives. So we need not subtract the answer from 1.