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19 September, 19:22

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

A. 97.06%

B. 47.14%

C. 97.1%

D. 97.2%

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  1. 19 September, 19:38
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    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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