Question

Hi I have this example in my text book, it is based on normal distribution, I understand AI but not AII could someone please explain where there 100% and 00.85% come from? I will attach the page in a sec. - Thanks for the help

Answer 1

Here is the link: http://img836.imageshack.us/img836/7998/bac3c96ecc3444f784d95fd.png I have also attached it if you wish to download it.

Answer 2

*also in my original question i meant 99.85% not 00.85% :)

Answer 3

Question A i asks for the proportion of cans with volumes less than 375 ml

For company A, the mean volume is 378 ml. Being normally distributed (bell curve shape), we know 50% of the cans have more than this volume, and 50% have less than this

with a standard deviation of 1, 375 is 3 standard deviations lower than the mean 378
that is way to to left, in the "tail" of the curve. The area under this tail is about 0.15% of the total area under the curve.

for A ii, they ask for the proportion of cans with volumes greater than 381 ml
381 is 3 sigma above the mean, in the right "tail". About 0.15% of the cans are 3 std deviations above the mean.

One way to answer this is find the area of the curve below 3 sigma (98.85%)
the entire area under the curve is 100%, and if we subtract the area below 3 sigma we get 0.15%, the area under the curve to the right of 3 sigma.

Answer 4

Thank you so much!

Answer 5

If that wasn't clear, maybe this will help
http://www.khanacademy.org/math/probability/statistics-inferential/normal_distribution/v/introduction-to-the-normal-distribution

Answer 6

Thanks for that link I'll look at it .