Help solve this problem??

Question Description

A certain brand of light bulb has a life, before burn-out that is normally distributed with a mean of 3000 hours and a standard deviation of 200 hours. 

If one such light bulb is randomly selected and used in a warehouse where it will be left on continuously. What is the probability that it will last for at least 120 days (4 months)? Note: 120 days of continual use is 120*24=2880 hours.

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Final Answer

Thank you for the opportunity to help you with your question!

So then we're looking for the probability that it will last 2880 or MORE.

First let's find the Z value

Z = 2880 - 3000 / 200 = -120 / 200 = -0.6

According to the Z table of standard  normal distribution, -0.6 corresponds to a probability of 0.2743

But that's for a bulb lasting 2880hrs or LESS

For 2880hrs or MORE we have to subtract from 1

1 - 0.2743 = 0.7257

Please let me know if you need any clarification. I'm always happy to answer your questions.

VincentA123 (2409)
Cornell University

Awesome! Perfect study aid.