Question

Certain type of light bulbs has a mean lifespan of 21 hours and a standard deviation...

Certain type of light bulbs has a mean lifespan of 21 hours and a standard deviation of 2.25 hours. What is the probability that the total lifespan of 200 lightbulbs is less than 4100 hours?

Math   Statistics-And-Probability   
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Answer #1

= 21

= 2.25

n = 200

SE = /

= 2.25/

= 0.1591

= 4100/200 = 20.5

To find P(20.5):

Z = (20.5 - 21)/0.1591

= - 3.1427

By Technology, Cumulative Area Under Standard Normal Curve = 0.00083699

So,

Answer is:

0.00083699

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