Mathematics
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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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

VincentA123 (2409)
Cornell University
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Anonymous
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