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djbigsteph
11-27-2005, 09:47 PM
i really need help in sampling distributions can you help ?

JohnM
11-27-2005, 09:49 PM

djbigsteph
11-27-2005, 09:51 PM
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
11-27-2005, 09:57 PM
OK. You'll need to post the specific question that you are struggling with, and also include what you've attempted so far...

djbigsteph
11-27-2005, 10:00 PM
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 ?

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
11-27-2005, 10:06 PM
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....

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
11-27-2005, 10:33 PM
r u still with me ?

JohnM
11-27-2005, 10:36 PM
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
11-27-2005, 10:37 PM
thanks 4 for all of your help

quark
11-27-2005, 10:38 PM
The posts were merged. :)