- Thread starter djbigsteph
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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

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)

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