SOLUTION: 2. The new Twinkle bulb has a standard deviation of 35 hours. A random sample of 50 light bulbs is selected from inventory. The sample mean was found to be 550 hours * can u show

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Question 483482: 2. The new Twinkle bulb has a standard deviation of 35 hours. A random sample of 50 light bulbs is selected from inventory. The sample mean was found to be 550 hours
* can u show me how to get the answers also with work?
a. What is the margin of error [E] for a 90% confidence interval? Round your answer to the nearest hundredths (5 points)

b. Construct a 90% confidence interval for the mean life of all Twinkle bulbs. (5 points)

3. A standard placement test has a mean of 115 and a standard deviation of 10. What is the minimum sample size required if we want to construct the 90% confidence interval with the margin of error of 2 points?
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Answer by edjones(8007) (Show Source):
You can put this solution on YOUR website!
3)
mean+-alpha/2(s/sqrt(n)=mean+-2
+-1.645(s/sqrt(n)=+-2 Subtract the mean from each side.
+-(1.645*10)/sqrt(n)=+-2
+-2sqrt(n)=+-16.45
+-sqrt(n)=+-8.225
n=67.65 square each side.
n=68
.
Ed