Question

The average weight of a chicken egg is 2.25 ounces with a standard deviation of 0.2 ounces. You take a random sample of a dozen eggs.

a) What is the probability that the mean weight of the eggs in the sample will be less than 2.2 ounces?

Answer 1

@TuringTest @thomaster

Answer 2

they give you the population standard deviation.
can you figure out the *sample* standard deviation for a sample size of 12 ?

Answer 3

that would be 0.2/sqrt (12) = 0.0577 right?

Answer 4

I think to find the probability would be
(x-mean)/standard deviation then I have to find out where it would be on the z table... am I correct?

Answer 5

yes, now how many sample std dev away is 2.2 from 2.25

Answer 6

-0.05

Answer 7

-0.05/0.0577

Answer 8

in normal distributions we *always* change differences into differences divided by the std dev.

Answer 9

you get 2.2 is -0.866 std dev below the mean

last step is figure out what area under the bell curve between -infinity and -0.866
one way is use this calculator
http://maartendecat.be/home/projects/online-normal-distribution-calculator/