# statistics

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1. The new Twinkle bulb has a standard deviation σ = 34 hours. A random sample of 77 light bulbs is selected from inventory. The sample mean was found to be x= 492 hours.
Question: Find the margin of error E for a 90% confidence interval.

n = 77, 492, σ = 34, zc = 1.645
1.645 x 34/√77 = 6.37

Question: Construct a 90% confidence interval for the mean life, µ of all Twinkle
bulbs.

n = 77, 492, σ = 34, zc = 1.645
492 – 6.37 = 485.63
492 + 6.37 = 498.37

485.63 < µ < 498.37

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