Question

The average 60-watt (a unit of power) bulb emits about 800 lumens (a measure of brightness) of light. Suppose the population standard deviation is 30 lumens. Also suppose you're testing a new watt bulb to see if it emits more light with the same 60 watts of power. With a sample of 100 bulbs and 99% confidence, what is the minimum average your sample can have and still be counted as statistically significant?

Answer 1

=800  =30  n=100

Z critical for 99% is 2.58 For two tailed

Z= Xbar-mu/sigma/sqrt(n)

Z= xbar-800/30/sqrt(100)

2.58= xbar-800/3

2.58*3= xbar-800

xbar= 807.74 is minimum sample mean to be statistically significant.

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