Question
An electrical firm manufactures light bulbs that have a length of life that is normally distributed,...
An electrical firm manufactures light bulbs that have a length of life that is normally distributed, with mean equal to 800 hours and a standard deviation of 40 hours. Suppose a 100 light bulbs are randomly selected for testing the length of life. Let x ̅ represent the sample mean length of life of the light bulbs.
σ_( x ̅ ) = 4 hours
n) Find a lower and an upper mean length of life of bulbs in hours such that 90% of all values of the sample mean length of life of light bulbs computed from random samples of size 100 lie in this interval.
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