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August 28, 2015

Homework Help: statistics

Posted by looking for someone to varify my work please on Tuesday, April 6, 2010 at 3:56pm.

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.

Round your answer to the nearest hundredths.

Answer:
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, of all Twinkle
bulbs.

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

485.63 < < 498.37

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