The useful life of a certain type of light bulb is known to have a= 40 hours. Hoe large a sample should be taken standard deviation of it is desired to have a margin of error of 10 hours or less at a 95% level of confidence?
useful life =40 hours
Margin of Error= 10 hours
At 95% level of confidence
"n=(\\frac {(z)(\\sigma)}{MOE})^2"
For 95% level of confidence, standard deviation "\\sigma" = 0.05
"\\therefore" "n=(\\frac {(40)(0.05)}{10})^2"
"=0.04"
"\\implies"Interval of the sample ranges up to 0.04 (overall upper limit)
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