The mean and standard deviation of the lifetimes of 9 randomly
selected Duracell batteries are 42...
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The mean and standard deviation of the lifetimes of 9 randomlyselected Duracell batteries are 42 days and 20 days, respectively.The mean and standard deviation of the lifetimes of 11 randomlyselected Eveready batteries are 45 days and 17 days, respectively.Suppose that the lifetime of a Duracell battery has NORM(μ_X,σ^2 )and the lifetime of an Eveready battery has NORM(μ_Y,σ^2 ).
a) Find an unbiased estimate of σ^2.
b) Calculate an 96% confidence interval for μ_X-μ_Y.
c) Test whether the mean lifetime of all Duracell batteries isless than the mean lifetime of all Eveready batteries. State thenull and alternative hypotheses, determine the critical region,make a decision based on α=0.05 and write your conclusion.
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for sample 1 n19 X1bar42 sd120 Same way for sample 2 n211 X2bar45 sd217 b For 96 conf level of mean we
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