SOLUTION: Hi, I was wondering if I could get some help understanding how to do this question: How long do new batteries last on a camping trip? n1 = 42 random small camp flashlights w

Question 619946: Hi, I was wondering if I could get some help understanding how to do this question:

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. 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 for
lifetimes was x = 8.1 hours. Historical data suggests that σ1 = 2.2 hours and σ2 = 3.5 hours. Find a 90% confidence interval for the population difference of lifetimes for
these batteries.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
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.
=====================================================
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.
-----------------------------------------------------------------------
Find a 90% confidence interval for the population difference of lifetimes for
these batteries.
---
I used the 2-SampleZInterval function on my TI-84 to get this 90% conf. int.:
(0.6119 , 2.7881)
=======================
Cheers,
Stan H.
=======================

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