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A company installs 5000 light bulbs, each with an average life of 500 hours, standard deviation of 100 hours, and distribution approximated by a normal curve. Find the percentage of bulbs that can be expected to last the period of time. Less than 690 hours

A97.06%

B47.14%

C97.1%

D97.2%

Verified Answer :

nobillionaireNobley

Let X be a random variable representing the number of hours a bulb is expected to last.
P(X < 690) = P(z < (690 - 500)/100) = P(z < 190/100) = P(z < 1.9) = 0.97128 = 97.1%

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