Question 619946
How long do new batteries last on a camping trip? 
n1 = 42 random small camp flashlights were fitted with brand 1 batteries and left on until the batteries failed. 
The sample mean lifetime was x = 9.8 hours. 
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Another n2 = 38 random small flashlights of the same model 
were fitted with brand II batteries and left on until the batteries failed. The sample mean forlifetimes was x = 8.1 hours. 
Historical data suggests that σ1 = 2.2 hours and σ2 = 3.5 hours. 
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Find a 90% confidence interval for the population difference of lifetimes for 
these batteries.
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I used the 2-SampleZInterval function on my TI-84 to get this 90% conf. int.:
(0.6119 , 2.7881)
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Cheers,
Stan H.
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