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September 15, 2014

September 15, 2014

Posted by **Ryan** on Monday, January 31, 2011 at 3:45am.

What is the probability that the sample mean lifetime will be between 105 and 115 hours?

0.4306

0.3026

0.1974

0.7372

0.8612

What value does the sample mean exceed with 95% probability (Hint: This is the 5th percentile for the sample mean distribution)?

77.10

106.79

104.44

116.63

115.56

- Stats -
**drwls**, Monday, January 31, 2011 at 10:17amFor an individual bulb, the probability of a life between 105 and 115 hours is 0.1974. I used a normal probability calculator to get that.

For 35 bulbs, the mean of the average remains 110 but the standard deviation is 20/sqrt35 = 3.38. The probabilty of the mean being between 105 and 115 is then 0.861.

For your second question, I get 104.4

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