# What is the z-score of sample X, if n = 256, mu= 42, St. Dev. =80, and mu_X =89?

$z = \frac{47}{5} = 9.4$

#### Explanation:

Use the formula

$z = \frac{{\mu}_{x} - \mu}{\left(\frac{\sigma}{\sqrt{n}}\right)} = \frac{89 - 42}{\left(\frac{80}{\sqrt{256}}\right)} = \frac{47}{\left(\frac{80}{16}\right)} = \frac{47}{5}$

$z = 9.4$

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