sampling distributions

[djbigsteph]

i really need help in sampling distributions can you help ?

[JohnM]

Possibly.....please post a question and we'll do our best to help you out.:)

[djbigsteph]

i really need help in sampling distributions can you help ?
ok i am having difficulty solving for the sample mean when it is not given. what do i do ?

i also need help with normal cumulative distribution too

[JohnM]

OK. You'll need to post the specific question that you are struggling with, and also include what you've attempted so far...

[djbigsteph]

general electric produces a soft white 100 watt bulb for which it states that the average life is 750 hours. Assume the deviation is 120 hours.

Suppose a consumer agency randomly selects 100 of theses bulbs and finds a sample mean life of 735 hours. should the consumer agency doubt the manufacturer's claim ?

i should first calculate z -score

z=735-750/120 ?

my answer is -.125

please let me know if i am on the right track ?

r uthere ?

sorry i did not know

i checked my z -table and i got .45

.45 is greater than .05 so ho is true ?

i have one more question about range

Suppose scores on a national test follow a normal distribution with mean of 600 and standard deviation of 100.
What sample size would be required such that 95% of the possible sample means would be 20 points from the population mean.
explain how to calculate i am really stuck

[JohnM]

Try not to submit a lot of posts - just put all of your thoughts in one - it makes it a lot easier to follow...this is not the same as IM or chat....


First set up your hypotheses-

Ho: mu = 750
Ha: mu < 750

then set your alpha level (significance level) - usually this is .10, .05, or .01 and is your choice if not specified (usually .05 is chosen)

then compute z:

z = (x - mu) / SE
where SE = s/sqrt(n)

then look up the probability of z in the normal distribution tables - if p(z) is <= alpha, then you have sufficient evidence to reject Ho (reject general electric's claim of mean life of 750 hrs)

[djbigsteph]

r u still with me ?

[JohnM]

I'm still online, but the site administrator deleted a lot of your posts - don't expect an immediate response just because we're online - often I'm working on something else or away from my computer....

Just post your question and we'll try to get back within a reasonable amount of time - could be immediately, but also could be up to 1-2 days.

[djbigsteph]

thanks 4 for all of your help

[quark]

The posts were merged. :)