The guaranteed average life of a certain type of electric light bulb is 1000 hrs with a standard deviation of 125hrs. It is decided to sample the output so as to ensure that 90% of the bulbs do not fall short of the guaranteed average by more than 2.5% find the minimum sample size.
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Given:
guaranteed average life
standard deviation
As we do not want the sample mean to be less than the guaranteed average mean by more than 2.5 %
To Find:
minimum sample size
Solution:
We know that
Assume be the given sample size.
Then,
The sample is large
Use the given condition:
The minimum sample size is 25.
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