2. The new Twinkle bulb has a standard deviation hours. A random sample of 77 light bulbs is selected from inventory. The sample mean was found to be 492 hours.
a. Find the margin of error E for a 90% confidence interval.
Round your answer to the nearest hundredths.

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  1. Margin of error = z-value (sd/√n)

    Find the z-value corresponding to 90% confidence using a z-table.

    sd = standard deviation
    n = sample size

    I hope this will help get you started.

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  2. Please someone help me? The new twinkle bulb has a standard deviation 35 hours. A random sample of 50 light bulbs is selected from inventory. The sample mean was found to be x=500 hrs. Find the margin of error for 95%, construct a 95% confidence interval for the mean life of all Twinkle bulbs. I am desperate.

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