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almond37 [142]
3 years ago
9

A standard fluorescent tube has a life length that is normally distributed with a mean of 7000 hours and a standard deviation of

1000 hours. A competitor has developed a compact fluorescent lighting system that will fit into incandescent sockets. It claims that a new compact tube has a normally distributed life length with a mean of 7500 hours and a standard deviation of 1200 hours.
1. Which fluorescent tube is more likely to have a life length greater than 9000 hours?
Mathematics
1 answer:
adell [148]3 years ago
7 0

Answer:

The new compact tube is more likely to have a life length greater than 9000 hours.

Step-by-step explanation:

Problems of normally distributed samples are solved using the z-score formula.

In a set with mean \mu and standard deviation \sigma, the zscore of a measure X is given by:

Z = \frac{X - \mu}{\sigma}

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.

In this problem, we have that:

Standard tube:

\mu = 7000, \sigma = 2000

New compact tube:

\mu = 7500, \sigma = 1200

1. Which fluorescent tube is more likely to have a life length greater than 9000 hours?

Whichever tube has the lower z-score when X = 9000, since the probability of having a life length greater than 9000 hours is 1 subtracted by the pvalue of Z when X = 9000. The higer z, the higher it's pvalue.

Standard tube:

Z = \frac{X - \mu}{\sigma}

Z = \frac{9000 - 7000}{1000}

Z = 2

New compact tube:

Z = \frac{X - \mu}{\sigma}

Z = \frac{9000 - 7500}{1200}

Z = 1.25

The new compact tube is more likely to have a life length greater than 9000 hours.

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