(a) Sample mean is expected to be the same. (Standard Error of the mean) SEm = SD/√n
(b) Assume equal times. One bulb = 500 hours.
Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability of the Z score.
If the events are independent, the probability of both/all events occurring is determined by multiplying the probabilities of the individual events.
The lifetime of a type of electric bulb has expected value µ = 475 hours and standard deviation
σ = 60 hours.
(a) Use the central limit theorem to determine the expected value and standard deviation of the
sample mean of n such lightbulbs where n = 100, 200, or 400.
(b) You buy two such lightbulbs, use one, and when it expires, you replace it by the other. Assuming
that the lifetimes of the two lightbulbs are independent, what is the probability that the two
lightbulbs have a combined lifetime of over 1000 hours
1 answer
1 answer