Question

A light bulb company advertises that a 75-watt light bulb has an average life of 500 hours with a standard deviation of 30 hours.

What is the z-score of a light bulb lasting 425 hours?

-2.2
-2.5
-1.9
-1

Answer 1

Therefore, the z-score of a light bulb lasting 425 hours is -2.5.

Explanation:

To calculate the z-score, you need to use the formula:

z = (X - μ) / σ

Where:

X = the value you want to find the z-score for (425 hours in this case)

μ = the mean (average) value (500 hours in this case)

σ = the standard deviation (30 hours in this case)

Using the given values, the z-score can be calculated as:

z = (425 - 500) / 30

z = -2.5

Therefore, the z-score of a light bulb lasting 425 hours is -2.5.

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