Solution to An electrical firm manufactures light bulbs that have a length of life that is approximately … - Sikademy
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Archangel Macsika

An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed, with mean equal to 810 hours and a standard deviation of 92 hours. Find the probability that a random samples of 39 bulbs will have an average life of less than 783 hours

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Let X= the average life: X\sim N(\mu, \sigma^2/n).

Given \mu=810\ h, \sigma=92\ h, n=39.


P(X<783)=P(Z<\dfrac{783-810}{92/\sqrt{39}})

\approx P(Z<-1.832771)\approx0.0334

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Question ID: mtid-4-stid-46-sqid-2459-qpid-929