Question

100 air conditioners were tested and it was found that the average power usage per hour during the summer months (for around 9 hours per day) is 4100 W.

Find the 90% confidence interval if   = 60 W.

Find the lower confidence limit

Find the upper confidence limit

Answer 1

z @ 90.0% = 1.6449

Required confidence interval = (4100.0-1.6449(6.0), 4100.0+1.6449(6.0))
Required confidence interval = (4100.0 - 9.8694, 4100.0 + 9.8694)
Required confidence interval = (4090.1306, 4109.8694)
lower confidence limit = 4090.1306
upper confidence limit = 4109.8694

Interpretion: We are 90.0% confident that the true mean of the population lie between the interval 4090.1306 and 4109.8694.

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