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